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Model Answer M Sc II Sem Zoology
2013
LZT- 204 Mammalian Physiology & Endocrinology
Section A: Multiple Choice questions (Tick the appropriate answer)
(10 X 2)
(1)
Formation of bilirubin takes place in: (c) 2, 3, 4
(2)
Which of the following represents the correct pathway for conduction of an action
potential through the heart:(c) SA node, AV node, AV bundle, bundle branches,
Purkinje fibers
(3)
Chief cells secrete:
(4)
Fructose is transported by: (b) Facilitate diffusion
(5)
Brain stem not includes: (d) cerebellum
(6)
Spinal cord connects to the brain through the:(b) foraman magnum
(7)
Which one is a neurotoxin (b) Tetrodotoxin
(8)
Which are neurotransmitters (a) Acetylcholine, Epinephrine and Dopamine
(9)
Unit of pineal gland is (a) Pinealocyte
(10)
The average plasma half-life of insulin is (b) 6 min
(c) Pepsinogen and gastric lipase
Section B
Q 2:
Descriptive type (Answer any four question within 200 words)
Question 1:
(10 X4)
Describe the formation of platelets from pluripotent stem cell, including the
influence of hormone? (6+4)
Answer:
Red bone marrow is located in the spongy bone tissue. It is present in the bones of axial skeleton,
pectoral and pelvic girdles, proximal epiphysis of the humerus and femur. About 0.05-0.1% of
red bone marrow cells are derived from mesenchyme and are called pluripotent stem cells or
hemocytoblast. These cells have capacity to develop in to many different type of cells, including
platelets. Pluripotent cells in red bone marrow produces two type of stem cell, which have the
capacity to develop into several types of cells. These stem cells are called myeloid stem cells and
lymphoid stem cells. Myeloid stem cell begins their development in red bone marrow and gives
rise to red blood cells, platelets and few WBCs. During hemopoiesis, some of the myeloid stem
cells differentiated into progenitor and precursor cells. Progenitor cells giving rise to more
specific element of blood and also called as colony forming units (CFUs). CFU-Meg produces
megakaryocytes, the source of platelets.
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
Thrombopoietin or TPO is a hormone produced by the liver that stimulates the formation of
platelets from megakaryocytes. Under the influence of the hormone thrombopoietin, myeloid
stem cells develop into precursor cells called megakaryoblasts. Megakaryoblast transform into
megakaryocytes, huge cells that splinter inyo 2000 to 3000 fragment. Each fragment, enclosed
by a piece of the plasma membrane is a platelet or thrompocyte. Platelets break off from the
megakarytocytes in red bone marrow and then enter the blood circulation. Between 150,000 to
400,000 platelets are present in each µl of blood. Each is disc shaped, 2-4 µm in diameter, and
has many vesicles and no nucleus.
Question 2:
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Describe the mechanism of digestion of carbohydrates, protein and lipid in small
intestine? (3+4+3)
Answer:
In mouth, salivary amylase converts starch to maltose, maltotriose and α-dextrin. In the stomach,
pepsin converts proteins to peptides and lingual and gastric lipase converts some triglycerides
into fatty acids, triglycerides and mono glycerides. When chime entering in the small intestine
contains partially digested carbohydrate, protein and lipid. The completion of the digestion of
carbohydrates, proteins and lipids takes place collectively by pancreatic, bile and intestinal juice.
Digestion of carbohydrates:
Those starches not broken down into maltose, maltotriose and α-dextrin are cleaved by
pancreatic amylase.
Pancreatic amylase:
Starch and glycogen →
maltose, maltotriose and α-dextrin
Ingested molecule of sucrose, lactose and maltose are only acted in the small intestine.
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
Three brush border enzymes digest the disaccharides into monosaccharide. Sucrase breaks
sucrose into a molecule of glucose and a molecule of fructose; lactase digests lactose into a
molecule of glucose and a molecule of galactose; and maltase splits maltose and maltotriose in to
two or three molecule of glucose.
Sucrase:
Lactase:
Maltase:
Sucrose
Lactose
Maltose
or maltotriose
→
→
→
glucose + fructose
glucose + galactose
two or three molecule of glucose.
Digestion of carbohydrates ends with production of monosaccharide.
Digestion of proteins:
Protein digestion starts in the stomach, where proteins are fragmented intp peotides by the action
of pepsin. Protein digestive enzymes of pancreatic juice include trysin, chymotrypsin,
carboxytrypsin and elastase. All these enzymes convert whole protein into peptides in the small
intestine. Trysin, chymotrypsin and elastase cleave the peptide bond between a specific amino
acid, whereas carboxypeptidase split off the amino acid at the carboxyl end of a peptide. Protein
digestion is completed by two peptides in the brush border i.e., aminopeptidase and dipeptidase.
Aminopeptidase cleaves off amino acid at the amino end of a peptide. Dipeptidase splits
dipeptides into single amino acids.
Aminopeptidase:
Amino acid at the amino end of a peptide → Amino acid and peptides
Dipeptidase:
Dipeptides → Amino acids.
Digestion of lipids:
Lipid digestion starts at in the stomach by the action of lingual and gastric lipase. Triglycerides
are broken down by pancreatic lipase into fatty acids and monoglycerides in the small intestine.
Large lipid globule containing triglyceride first undergoes emulsification then digested in the
small intestine. The hydrophobic regions of the bile salts interact with the large lipid globule,
while the hydrophilic regions of the bile salts interact with the watery intestinal chime.
Consequently, the large lipid globule is broken down into several small lipid globules, about 1
µm in diameter.
Pancreatic lipase:
Triglycerides →
Fatty acids + Monoglycerides
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Question 3:
Answer:
Describe the event that causes inhalation and exhalation? (10)
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
Exhalation is the flow of the respiratory current out of the organism. In humans it is the
movement of air out of the bronchial tubes, through the airways, to the external environment
during breathing. This happens due to elastic properties of the lungs, as well as the internal
intercostal muscles which lower the rib cage and decrease thoracic volume. As the thoracic
diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and
put pressure on the lungs to expel the air. During forced exhalation, as when blowing out a
candle, expiratory muscles including the abdominal muscles and internal intercostal muscles
generate abdominal and thoracic pressure, which forces air out of the lungs. Exhaled air is rich in
carbon dioxide, a waste product of cellular respiration during the production of energy, which is
stored as ATP. Exhalation has a complementary relationship to inhalation; the cycling between
these two efforts define respiration.
The main reason for exhalation is to rid the body of carbon dioxide, which is the waste product
of gas exchange in humans. Air is brought in the body through inhalation. During this process air
is taken in through the lungs. Diffusion in the alveoli allows for the exchange of O2 into the
pulmonary capillaries and the removal of CO2 and other gases from the pulmonary capillaries to
be exhaled. In order for the lungs to expel air the diaphragm relaxes, which pushes up on the
lungs. The air then flows through the trachea then through the larynx and pharynx to the nasal
cavity and oral cavity where it is expelled out of the body. Exhalation takes longer than
inhalation since it is believed to facilitate better exchange of gases. Parts of the nervous system
help to regulate respiration in humans.
Exhalation is either passive or active, depending on the level of respiratory activity. When
exhalation is active, it may involve one or more of the following muscles. The internal
intercostal and transversus thoracis muscles depress the ribs and reduce the width and depth of
the thoracic cavity. The abdominal muscles, including the external and internal oblique,
transversus abdominis, and rectus abdominis muscles, can assist the internal intercostal muscles
in exhalation by compressing the abdomen and forcing the diaphragm upward.
Inhalation is the flow of the respiratory current into an organism. In humans it is the movement
of air from the external environment, through the airways, and into the alveoli. Inhalation begins
with the contraction of the muscles attached to the rib cage; this causes an expansion in the chest
cavity. Onset of contraction of the diaphragm results in expansion of the intrapleural space and
an increase in negative pressure. This negative pressure generates airflow because of the pressure
difference between the atmosphere and alveolus. Air enters, inflating the lung through either the
nose or the mouth into the pharynx (throat) and trachea before entering the alveoli.
Inhalation is an active process involving the contraction of one or more of these muscles. The
contraction of the diaphragm increases the volume of the thoracic cavity by tensing and
flattening its floor, and this increase draws air into the lungs. Diaphragmatic contraction is
responsible for air movement in normal breathing at rest. The external intercostal muscles assist
in inhalation by elevating the ribs. Accessory muscles, including the sternocleidomastoid,
serratus anterior, pectoralis minor, and scalene muscles, can assist the external intercostal
muscles in elevating the ribs. These muscles increase the speed and amount of rib movement.
Model Answer M Sc II Sem Zoology
Question 4:
LZT- 204 Mammalian Physiology & Endocrinology
2013
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Define hormonal regulation of tubular reabsorption and tubular secretion? (6+4)
Answer:
To maintain a precise balance between tubular reabsorption and glomerular filtration, there are
multiple nervous, hormonal and local control mechanisms that regulate tubular reabsorption. An
important feature of tubular reabsorption is that reabsorption of some solutes can be regulated
independently of others, especially through hormonal control mechanisms. Five hormones affect
the extent of Na+, Cl-, Ca++ and water reabsorption as well as K+ secretion by the renal tubule.
These hormones include angiotensin II, aldosterone, antidiuretic hormone atrial natriuretic
peptide and parathyroid hormone.
Renin–Angiotensin-Aldosterone System
The renin-angiotensin system (RAS) or the renin-angiotensin-aldosterone system (RAAS) is a
hormone system that regulates blood pressure and water (fluid) balance. When blood volume is
low, juxtaglomerular cells in the kidneys secrete renin directly into circulation. Plasma renin then
carries out the conversion of angiotensinogen released by the liver to angiotensin I. Angiotensin I
is subsequently converted to angiotensin II by the enzyme angiotensin converting enzyme found
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
in the lungs. Angiotensin II is a potent vaso-active peptide that causes blood vessels to constrict,
resulting in increased blood pressure. Angiotensin II also stimulates the secretion of the hormone
aldosterone from the adrenal cortex. Aldosterone causes the tubules of the kidneys to increase
the reabsorption of sodium and water into the blood. This increases the volume of fluid in the
body, which also increases blood pressure. The system can be activated when there is a loss of
blood volume or a drop in blood pressure (such as in hemorrhage or dehydration). This loss of
pressure is interpreted by baroreceptors in the carotid sinus. In alternative fashion, a decrease in
the filtrate NaCl concentration and/or decreased filtrate flow rate will stimulate the macula densa
to signal the juxtaglomerular cells to release renin.
Aldosterone:
Aldosterone is a steroid hormone (mineralocorticoid) produced by the outer section (zona
glomerulosa) of the adrenal cortex in the adrenal gland. It acts mainly on the distal tubules and
collecting ducts of the nephron, the functional unit of the kidney, to cause the conservation of
sodium, secretion of potassium, increased water retention, and increased blood pressure. The
overall effect of aldosterone is to increase reabsorption of ions and water in the kidney increasing
blood volume and, therefore, increasing blood pressure.
Antidiuretic hormone (ADH):
It is also known as vasopressin and argipressin that is a neurohypophysial hormone found in
most mammals. Its two primary functions are to retain water in the body and to constrict blood
vessels. Vasopressin regulates the body's retention of water by acting to increase water
absorption in the collecting ducts of the kidney nephron. Vasopressin increases water
permeability of the kidney's collecting duct and distal convoluted tubule by inducing
translocation of aquaporin-CD water channels in the kidney nephron collecting duct plasma
membrane. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
tubules of the kidneys by affecting the tissue's permeability. It also increases peripheral vascular
resistance, which in turn increases arterial blood pressure. It plays a key role in homeostasis, by
the regulation of water, glucose, and salts in the blood. It is derived from a preprohormone
precursor that is synthesized in the hypothalamus and stored in vesicles at the posterior pituitary.
Most of it is stored in the posterior pituitary to be released into the bloodstream. However, some
AVP may also be released directly into the brain, and accumulating evidence suggests it plays an
important role in social behavior, sexual motivation and bonding, and maternal responses to
stress.
Atrial Natriuretic Peptide:
A large increase in blood volume promotes release of the atrial natriuretic peptide from the heart.
It can inhibit reabsorption of Na+ and water in the proximal convoluted and collecting duct. ANP
also suppress the secretion of aldosterone and ADH. These effects increase the excretion of Na +
in urine and increase urine output, which decreases blood volume and blood pressure.
Parathyroid hormone:
A lower than normal level of Ca++ in the blood stimulates the parathyroid gland to release
parathyroid hormone (PTH) PTH in turn stimulates cells in the early distal convoluted tubules to
reabsorb more Ca++ into the blood. PTH also inhibit HPO4- - reabsorption in proximal convoluted
tubules, thereby promoting the phosphate excretion
Question 5:
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List the sequence of events that generate an action potential?
Answer:
The action potential is dramatic redistribution of electrical charge across the membrane.
Depolarization of the cell during the action potential is caused by the influx of sodium ions
across the membrane and the repolarization is caused by the efflux of potassium ions. An action
potential is a short lasting event in which the electrical membrane potential of a cell rapidly rises
and falls, following a consistent trajectory. Action potentials occur in several types of animal
cells, called excitable cells, which include neurons, muscle cells and endocrine cells. In neurons,
they play a central role in cell-to-cell communication. In other types of cells, their main function
is to activate intracellular processes. In muscle cells, for example, an action potential is the first
step in the chain of events leading to contraction.
Action potentials in neurons are also known as "nerve impulses" or "spikes", and the temporal
sequence of action potentials generated by a neuron is called its "spike train". A neuron that
emits an action potential is often said to "fire". Necessary amount of any stimulus known as
“threshold” that is needed to change the inner membrane potential -70mV to -55mV. This
changes of membrane potential happened due to open Na + channels. The resting potential in
excitable cells is usually near -55 mV. More depolarized voltages would lead to spontaneous
generation of action potentials. Once the threshold value change the membrane potential-70mv
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
to-55mV, in response of voltage, opens the voltage sensitive Na+ channels, so influx of Na+
occurs. In response of depolarization or +55mV, voltage sensitive K+ channels became open and
cause the efflux of K+. Due to efflux of K+ nerve fragments became repolarized (-70mV).
Excessive efflux of K+ due to leaky K+ channel cell becomes hyperpolarized (-90mV).
Several steps responsible for generation of action potential:

At resting potential, a majority of the sodium-gated channels are closed. A few of the
potassium channels are open, but a majority remains closed.

As stimulation causes depolarization, gated sodium-channels open up, allowing the
inflow of sodium ions, creating a state of depolarization. This result in more gated
sodium channels opening up, thereby increasing the inflow of sodium ions into the cell,
further depolarizing the membrane.

The rising phase occurs when the threshold is crossed and the positive feedback cycle
quickly returns the membrane potential closer to the equilibrium potential of the sodium
ion.

The inactivation of the voltage-gated sodium channels and rapid outward flow of
potassium ions through the opened voltage-gated potassium channels rapidly return the
membrane potential closer to the equilibrium potential of a potassium ion. Hence, this
phase is called the falling phase.

The membrane potential is closer to the equilibrium potential of a potassium ion as there
is an increased permeability to potassium ions. When potassium channels close, the
membrane returns to its resting potential.
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013

The sodium channels stay inactivated throughout the falling phase and undershoot. If a
second depolarizing stimulus happens during this time period, it is not able to generate an
action potential. The time when a second action potential cannot be generated is called
the refractory period.

The period, after excitation, during which a membrane recovers it polarization and is not
able to respond to a second stimulus
Action Potential has certain identifiable part or key properties to explain it such as Threshold
value, Rising Phase, Overshoot Phase, Falling Phase, Undershoot Phase and Absolute refractory
period.
The main steps in the generation of an action potential?
1. Resting potential: all voltage-gates are closed.
2. At threshold, Sodium activation gate opens and Sodium permeability rises.
3. Sodium enters the cell (influx), causing an explosive depolarization to +30 mV, which
generation the rising phase of action potential.
4. At peak of action potential, sodium activation gate closes and sodium permeability falls,
which reduces the net movement of sodium into the cell. At the same time potassium activation
gate opens and potassium permeability rises.
5. Potassium leaves the cell (efflux), causing the repolarization to resting potential, which
generates the falling phase of action potential.
6. On return to resting potential, sodium activation gates closes and inactivation gates opens,
resetting channel for another depolarizing triggering event.
7. Further outward movement of potassium through still open potassium channels briefly
hyperpolarize membrane.
8. Potassium activation gate closes and membrane returns to resting potential
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Model Answer M Sc II Sem Zoology
Question 6:
LZT- 204 Mammalian Physiology & Endocrinology
2013
What are the octapeptides? Describe the structure and function of octapetides.
Answer:
Octapeptideare the hormones aynthesized in the supraoptic and paraventricullar hypothalamic nuclei
Octapetide consists of nine amino acid residue, but since two cysteine residue are are joined by disulphide
bridge and result in the formation of cysteine hence they are called and octapeptide rather than
nanopeptide. These hormone are stored in the pars nervosa until they released in the general circulation.
There are two octapeptidedhormoenpresent in pars nervosa
1. ArgininVasopressin
2. Oxytocin
1.Arginin Vasopressin
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
Amino acid sequence of arginine vasopressin is Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly, with the
cysteine residues forming a disulfide bond. Vasopressin is a peptide hormone that controls the
reabsorption of molecules in the tubules of the kidneys by affecting the tissue's permeability. It also
increases peripheral vascular resistance, which in turn increases arterial blood pressure. It plays a key role
in homeostasis, by the regulation of water, glucose, and salts in the blood. It is derived from
apreprohormone precursor that is synthesized in the hypothalamus and stored in vesicles at the posterior
pituitary. Most of it is stored in the posterior pituitary to be released into the bloodstream. Some AVP
may also be released directly into the brain, and accumulating evidence suggests it plays an important role
in social behavior, sexual motivation and bonding, and maternal responses to stress.
Secretion
The main stimulus for secretion of vasopressin is increased osmolality of plasma. Reduced volume of
extracellular fluid also has this effect, but is a less sensitive mechanism.
1. Vasopressin is produced by magnocellular neurosecretory neurons in the Paraventricular nucleus of
hypothalamus (PVN) and Supraoptic nucleus (SON). It then travels down the axon through
the infundibulum within neurosecretory granules that are found within Herring bodies, localized swellings
of the axons and nerve terminals. These carry the peptide directly to the posterior pituitary gland, where it
is stored until released into the blood. However there are two other sources of AVP with important local
effects:
2. AVP is also synthesized by parvocellularneurosecretory neurons at the PVN, transported and released
at the median eminence, which then travels through the hypophyseal portal system to the anterior pituitary
where it stimulates corticotropic cells synergistically with CRH to produce ACTH (by itself it is a weak
secretagogue). Vasopressin is also released into the brain by several different populations of smaller
neuron
Regulation/ function and control
Regulate the body's retention of water; it is released when the body is dehydrated and causes
the kidneys to conserve water, therefore, concentrating the urine and reducing urine volume. High
concentrations AVP, it also raises blood pressure by inducing moderate vasoconstriction. Has a variety of
neurological effects on the brain. Lysine vasopressin (LVP) or lypressin found in pigs very similar
substance with the same function and is used in human therapy.
Regulated the function of kidney
1. Increasing the water permeability of distal tubule and collecting duct cells in the kidney, thus
allowing water reabsorption and excretion of more concentrated urine, i.e., antidiuresis. Vasopressin,
acting through cAMP, also increases transcription of the aquaporin-2 gene, thus increasing the total
number of aquaporin-2 molecules in collecting duct cells.
2. Cyclic-AMP activates protein kinase A (PKA) by binding to its regulatory subunits and allowing them
to detach from the catalytic subunits. Detachment exposes the catalytic site in the enzyme, allowing it to
add phosphate groups to proteins (including the aquaporin-2 protein), which alters their functions.
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
3. Increasing permeability of the inner medullary portion of the collecting duct to urea by regulating the
cell surface expression of urea transporters which facilitates its reabsorption into the medullary
interstitium as it travels down the concentration gradient created by removing water from the connecting
tubule, cortical collecting duct, and outer medullary collecting duct.
Cardiovascular system
Vasopressin increases peripheral vascular resistance (vasoconstriction) and thus increases arterial blood
pressure. This effect appears small in healthy individuals; however it becomes an important compensatory
mechanism for restoring blood pressure in hypovolemic shock such as that which occurs during
hemorrhage.
Central Nervous system

It has been implicated in memory formation, including delayed reflexes, image, short- and longterm memory, though the mechanism remains unknown; these findings are controversial.
Vasopressin is released into the brain in a circadian rhythm by neurons of the supraoptic nucleus.

It acts in conjunction with corticotropin-releasing hormone to modulate the release
of corticosteroids from the adrenal gland in response to stress, particularly during pregnancy and
lactation in mammals.
2. OXYTOSIN
Its systematic name is cysteine-tyrosine-isoleucine-glutamine-asparagine-cysteine-proline-leucineglycine-amine (cys – tyr – ile – gln – asn – cys – pro – leu – gly – NH2, or CYIQNCPLG-NH2).
Oxytocin has a molecular mass of 1007 daltons and is highly conserved in placental mammals. Genomic
sequencing of the gene for oxytocin revealed a single in-frame mutation(thymine for cytosine) which
results in a single amino acid substitution at the 8-position (proline for leucine)
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
Function
Oxytocin plays roles in sexual reproduction, in particular during and after childbirth. It is released in large
amounts after distension of the cervix and uterus during labor, facilitating birth, maternal bonding, and,
after stimulation of the nipples, breastfeeding. Both-childbirth and milk ejection result from positive
feedback mechanisms.
1. Letdown reflex: In lactating (breastfeeding) mothers, oxytocin acts at the mammary glands, causing
milk to be 'let down' into sub areolar sinuses, from where it can be excreted via the nipple. Suckling by
the infant at the nipple is relayed by spinal nerves to the hypothalamus. The stimulation causes neurons
that make oxytocin to fire action potentials in intermittent bursts; these bursts result in the secretion of
pulses of oxytocin from the neurosecretory nerve terminals of the pituitary gland.
2. Uterine contraction: Important for cervical dilation before birth, oxytocin causes contractions during
the second and third stages of labor. Oxytocin release during breast feeding causes mild but often painful
contractions during the first few weeks of lactation.
3. This also serves to assist the uterus in clotting the placental attachment point postpartum.
3. Social behavior and wound healing: Oxytocin is also thought to modulate inflammation by decreasing
certain cytokines.
4. Oxytocin evokes feelings of contentment, reductions in anxiety, and feelings of calmness and security
around the mate. This suggests oxytocin may be important for the inhibition of the brain regions
associated with behavioral control, fear, and anxiety, thus allowing orgasm to occur. Oxytocin also
functions to protect against stress.
5. Due to its similarity to vasopressin, it can reduce the excretion of urine slightly. In several species,
oxytocin can stimulate sodium excretion from the kidneys (natriuresis), and, in humans, high doses can
result in hyponatremia.
3. Oxytocin and oxytocin receptors are also found in the heart in some rodents, and the hormone may play
a role in the embryonal development of the heart by promoting cardiomyocyte differentiation.
4. Modulation of hypothalamic-pituitary-adrenal axis activity: Oxytocin, under certain circumstances,
indirectly inhibits release of adrenocorticotropic hormone and cortisol and, in those situations, may be
considered an antagonist of vasopressin.
5. Oxytocin affects social distance between adult males and females, and may be responsible at least in
part for romantic attraction and subsequent monogamous pair bonding. An oxytocin nasal spray caused
men in a monogamous relationship.
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Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
7. Describe the anatomy and physiology of the male reproductive organ. How many steroids are
produced in mammalian male? Describe the pathway of their biosynthesis.
Answer:
Testis: Connective tissue septa divide testis into 250 lobules.Each lobule contains1-4
seminiferous tubules&interstitial connective tissue seminiferous tubules- produce sperm,
Interstitial tissue- leydig cells - produce testosterone. It also has a network of tubuleentry level
Rete testis and coiled tubular structure Efferent ductules which extends into Epididymis
Histomicrograph of testis
SPERMATIDS
2º SPERMATOCYTE
1º SPERMATOCYTE
SERTOLI
CELLS
Physiology Male Reproductive system
SPERMATOGONIA
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
2013
Sertoli cells stimulated by FSH and testosterone release androgen binding protein which binds
testosterone; thereby increasing testosterone concentration within the seminiferous tubules and
stimulating spermatogenesis
Follicle Stimulating Hormone (FSH): stimulates production of sperm in conjunction with
testosterone by regulating activity of Sertoli cells
Luteinizing Hormone (LH): stimulates testosterone production by Leydig cells
HYPOTHALAMUS REGULATES ACTIVITY OF ANTERIOR PITUITARY (ADENOHYPOPHYSIS
ADENOHYPOPHYSIS SYNTHESIZES HORMONES (LH and FSH) THAT MODULATE ACTIVITY OF
SERTOLI AND LEYDIG CELLS
NAME OF MAJOR STEROID HORMONE
a).Glucocorticoid
b). Mineralocorticoid
c). Testososterone/ Estrogen
d).Cortisol/ corticosterone
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
BIOSYNTHETIC PATHWAY OF STEROID HORMONES
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2013
Model Answer M Sc II Sem Zoology
LZT- 204 Mammalian Physiology & Endocrinology
***********
2013