Download Review for Medical Physiology

Review for Medical Physiology
Note: All contents in this file are just the key points. It is required that in the
examination students should give much more detailed description for every question.)
1. Regulation of body functions.
(1) Nervous regulation;
(2) Humoral regulation;
(3) Autoregulation.
2. Describe the ways of membrane transport.
(1) Simple diffusion;
(2) Facilitated diffusion;
(3) Active transport;
(4) Endocytosis and exocytosis.
3. Describe the physiological role of sodium pump.
(1) Maintaining the Na+ and K+ gradients across the cell membrane;
(2) Partly responsible for establishing a negative electrical potential inside the
cell;
(3) Controlling cell volume;
(4) Providing energy for secondary active transport
4. List the important factors in the establishment of the normal resting potential.
(1) K+ diffusion potential;
(2) Na+ diffusion;
(3) Na+-K+ pump
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5. Describe the mechanism of the initiation and termination of AP.
(1) Mechanism of the initiation of AP:
a. Local response and Na+ channel activated;
b. Regenerative cycle of Na+ influx;
c. Threshold potential.
(2) Mechanism of the termination of AP:
a. Na+ channel inactivated;
b. K+ channel activated.
6. Describe the molecular mechanism of muscle contraction.
(1) Increase of intracellular calcium level;
(2) Combination of calcium ion with troponin C;
(3) Conformational change of troponin complex and tropomyosin;
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(4) “Uncovery” of active sites of the actin;
(5) Interaction of myosin and actin filaments;
(6) Sliding mechanism, “walk-along” theory.
7. List the important factors that affect contractile performance of skeletal muscle.
(1) Preload;
(2) Afterload;
(3) Contractility.
8. Summarize the functions of red blood cells.
(1) Transport of O2 and CO2;
(2) Buffering.
9. Describe the physiological properties of platelets.
(1) Adhesion;
(2) Aggregation;
(3) Release.
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10. Name the common blood types, and describe how blood is typed and
cross-matched.
(1) The common blood types: A, B, AB, O;
(2) How is blood typed and cross-matched:
Blood typing
Sera
Red blood cell types
Anti-A
+
+
O
A
B
AB
Donor
Anti-B
+
+
Recipient
RBC
RBC
Plasma
Plasma
Cross-match
Test
11. Describe the blood clotting and anti-clotting systems and the clinical importance
of each system.
(1) Blood clotting system:
Blood coagulation system:
a. Intrinsic pathway;
b. Extrinsic pathway.
Clinical importance: mainly, prevention of bleeding.
(2) Anti-clotting system:
a. Intravascular anticoagulants:
a) Endothelial surface factors;
b) Antithrombin III;
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c) Heparin.
b. Fibrinolysis.
Clinical importance: Prevention of blood clotting, lysis of blood clots.
12. Describe in sequence the events that occur in the heart during cardiac cycle.
(1) Atrial systole;
(2) Isovolumic contraction phase;
(3) Rapid ejection phase;
(4) Reduced ejection phase;
(5) Isovolumic relaxation phase;
(6) Rapid filling phase;
(7) Reduced filling phase.
13. List the factors that affect heart pumping and the effect of each.
(1) Preload – Frank-Starling mechanism;
(2) Afterload;
(3) Myocardial contractility;
(4) Heart rate.
14. Describe the structure and function of the conduction system of the heart, and
compare the action potentials in each part of it with those in cardiac muscle.
(in very brief description)
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15. Draw a ventricular muscle cell action potential.
The depolarizing phase of the ventricular action potential is due mainly to a
positive-feedback increase in sodium permeability caused by the transient opening of
voltage-gated sodium channels. At almost the same time, the permeability to
potassium decreases as certain potassium channels close, which contributes to the
membrane depolarization. These potassium channels remain closed for about 0.15 s
(i.e., throughout most of the plateau phase of the action potential). This closure of
potassium-ion channels is partly responsible for the plateau phase, but in addition,
voltage-gated calcium channels open after a delay (calcium slow channels), allowing
calcium ions to flow into the cell and balance the outflow of potassium ions, which
keeps the membrane depolarized at the plateau level.
16. Describe the way the ECG is recorded and the waves of the ECG.
(1) The electrocardiogram (ECG) measures changes in skin electrical
voltage/potential caused by electrical currents generated by the heart.
(2) The waves of the ECG:
a. P wave: the sequential depolarization of the right and left atria;
b. QRS complex: right and left ventricular depolarization;
c. ST-T wave: ventricular repolarization;
d. U wave: origin for this wave is not clear - but probably represents
"afterdepolarizations" in the ventricles.
17. State the Poiseuille formula for flow in blood vessels, and explain on the basis of
this formula why the radius of a vessel is such an important determination of
flow.
(in very brief description)
Poiseuille’s formula: Q=Pr4/8L
18. List the factors affecting arterial blood pressure.
(1) Stroke volume;
(2) Heart rate;
(3) Peripheral resistance;
(4) Elastic vessels;
(5) Blood volume.
19. Describe the local control of blood flow.
(1) Acute control:
a. Tissue metabolism;
b. Oxygen available changes: Vasodilator Theory; Oxygen Lack Theory;
c. Other nutrients.
(2) Long-term control.
20. List the factors affecting formation of interstitial fluid.
(1) EFP = (Pc+ if) － (Pif+ P);
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(2) Rate of lymph flow;
(3) Capillary permeability.
21. Outline the neural mechanisms that control arterial blood pressure and heart rate,
including the receptors, afferent and efferent pathways, central integrating
pathway, and effector mechanisms involved.
(in very brief description)
(1) Autonomic nervous system;
(2) Vasomotor center;
(3) Higher nervous centers;
(4) Cardiovascular reflexes:
a. Baroreceptor reflex;
b. Chemoreceptor reflex;
c. Cardiopulmonary reflex;
d. CNS ischemic response.
22. List the principal vasoregulatory factors secreted by endothelial cells, and
describe the function of each.
(1) Vasodilator factors:
a. PGI2;
b. NO;
c. EDHF.
(2) Vasoconstrictor factors: Endothelin.
23. Name the principal hormones that affect arterial blood pressure, and know the
physiologic role of each.
(1) Angiotensin II:
a. Constricts resistance vessels
b. Acts upon the adrenal cortex to release aldosterone
c. Stimulates the release of vasopressin
d. Facilitates norepinephrine release from sympathetic nerve endings
e. Stimulates thirst centers within the brain
(2) Epinephrine and norepinephrine:
Effects
Epinephrine
Norepinephrine
Vessels
constriction (skin, visceral)
+
+++
relaxation (SM, liver)
－
+++
total peripheral resistance
±
+++
Blood pressure
systolic
+++
+++
diastolic
±
++
MAP
+
++
(3) Vasopressin:
a. Vasoconstriction, increase of arterial pressure;
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b. Antidiuretic effect.
(4) Atrial natriuretic peptide:
a. Produces natriuresis and diuresis
b. Decreases renin release
c. Reduces total peripheral resistance via vasodilatation
d. Decreases heart rate, cardiac output
(5) Opioid peptide:
a. Endorphin, Enkephalin, Dynorphin;
b. Complex cardiovascular effects.
(6) Kinin and histamine:
a. causes vasodilatation;
b. increases capillary permeability.
(7) Prostaglandins
24. Summarize the integrated, multifaceted system for arterial pressure regulation.
(1) Rapidly acting pressure control mechanisms acting within seconds or minutes;
(2) Pressure control mechanisms that act after many minutes;
(3) Long-term mechanism for arterial pressure regulation.
25. Describes the effects of PCO2, [H+] and PO2 on alveolar ventilation and their
mechanisms.
(1) CO2respiratory activity; Peripheral mechanism and central mechanism,
the latter is the main one.
(2) [H+]respiratory activity; Peripheral mechanism and central
mechanism, the latter is the main one.
(3) PO2respiratory activity; Peripheral mechanism is excitatory.
26. Explain the gastric secretion (including the composition and physiological
function of the gastric juice, the regulation of gastric secretion).
(1) Major components of gastric juice:
a. Hydrochloric acid:
i.
Acid sterilization;
ii.
Activation of pepsinogen;
iii.
Promotion of secretin secretion;
iv.
Assisted effect of iron and calcium absorption.
b. Pepsinogen: Pepsin activated from pepsinogen is an endopeptidase.
c. Mucus:
i.
Lubrication of the mucosal surface;
ii.
Protection of the tissue from mechanical damage by food particles.
d. Intrinsic factor: The intrinsic factor binds to Vit B12 and facilitates its
absorption.
(2) Regulation of gastric secretion:
a. Cephalic phase;
b. Gastric phase;
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c.
Intestinal phase.
27. Pancreatic secretion (including the composition and physiological function of the
pancreatic juice, the regulation of pancreatic secretion).
(1) Components of pancreatic juice:
a. Bicarbonate ions: Neutralizing acid entering the duodenum from the
stomach.
b. Pancreatic digestive enzymes:
i.
Carbohydrates: Pancreatic amylase;
ii.
Fat: Pancreatic lipase, Cholesterol esterase, Phospholipase;
iii.
Proteins:
Trypsinogen,
Chymotrypsinogen,
Procarboxypolypeptidase, Proelastase;
c. Trypsin inhibitor: Inhibits the activity of trypsin and thus guards against
the possible activation of trypsin and the subsequent autodigestion of the
pancreas.
(2) Regulation of pancreatic secretion:
a. Cephalic Phase;
b. Gastric Phase;
c. Intestinal Phase.
28. Biliary secretion (including the composition and physiological function of the
bile).
(1) Composition of bile:
a. HCO3b. Bile salts
c. Phospholipids
d. Cholesterol
e. Bile pigments
(2) Functions of bile:
a. Emulsifying or detergent function of bile salts
b. Bile salts help in the absorption of:
i.
Fatty acid
ii.
Monoglycerides
iii.
Cholesterol
iv.
Other lipids
29. Absorption in the small intestine.
(in very brief description)
30. Describe the digestion of carbohydrates, proteins and fat.
(in very brief description)
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1. List the factors that affect energy metabolic rate.
(1) Physical Activities
(2) Psychic activity
(3) Thermogenic effect of food
(4) Environmental temperature
2. Describe the modes of heat-loss from the skin.
(1) Radiation
(2) Conduction
(3) Convection
(4) Evaporation: Insensible evaporation and Evaporation of sweat
3. How dose the body actively maintain a constant body temperature despite changes in ambient
temperature?
When the hypothalamic temperature centers detect that the body temperature is either too high
or low due to the changes in ambient temperature, they institute appropriate body
temperature-decreasing or body temperature-increasing procedures to maintain a constant body
temperature.
Body temperature-decreasing procedures
(1) Vasodilatation
(2) Sweating
(3) Decrease in heat production
Body temperature-increasing procedures
(1) Skin vasoconstriction throughout the body
(2) Increase in heat production: Shivering, sympathetic excitation and thyroxin secretion
4. List the factors affecting glomerular filtration.
1) Glomerular hydrostatic pressure
Increased glomerular hydrostatic pressure increases GFR.
2) Colloid osmotic pressure of plasma
Increased colloid osmotic pressure of plasma decreases GFR.
3) Bowman's capsule pressure
Increased Bowman's capsule pressure decreases GFR.
4) Renal plasma flow
Increased renal plasma flow increases GFR.
5) Glomerular capillary filtration coefficient
Increased Glomerular capillary filtration coefficient increases GFR.
5. List the factors that affect the concentration and dilution of the urine.
1) Damage of renal medulla
Resulting in an impairment of the concentrating ability.
2) Loop diuretics
Such as frusemide, inhibiting the Na+/ K+/ 2Cl- cotransport system in the thick ascending
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limb, and reducing the osmotic gradient in the medulla.
3) Lack of urea in the body
Such as malnutrition, reducing the osmotic gradient established in the renal medulla.
4) Increased velocity of blood flow in the vasa recta
Certain vasodilators can markedly increase the velocity of blood flow in the vasa recta,
thereby carrying away amount of NaCl and reducing the osmotic gradient in the medulla.
6. What are the change of urine and its mechanism when one is injected intravenously 50%
glucose 100 milliliter?
The amount of the urine would increase.
After one is injected intravenously 50% glucose 100 milliliter, the amount of glucose filtered
from glomerulus exceeds tubular transport maximum for glucose. The osmotic effect of the
extra glucose remained in the renal tubules greatly decreases tubular reabsorption of water and
solute, and causes much loss of fluid into the urine.
7. What are the change of urine and its mechanism when one sweats a great deal and drinks little
water?
This would cause a small volume of concentrated urine to be excreted.
Sweat is a fluid of low osmotic pressure. When one sweats a great deal and drinks little water,
this would rapidly lead to an increase in plasma osmolarity and decreases in blood pressure and
blood volume. The former causes the osmoreceptor cells in the anterior hypothalamus to fire,
and the latter causes the arterial baroreceptor reflexes and the cardiopulmonary reflexes. Both
stimulate the synthesis and release of antidiuretic hormone (ADH). ADH is transported to the
kidneys, where it increases the water permeability of the late distal tubules, cortical collecting
tubules and inner medullary collecting ducts. This results in increased water reabsorption and
excretion of a small volume of concentrated urine.
In addition, water loss in sweat can also increase colloid osmotic pressure of plasma and
decrease net filtration pressure, leading to decreased glomerular filtration and decreased amount
of urine.
8. Describe the mechanism of accommodation of the eye.
1) Accommodation of lens
When an individual looks at a near object, the shape of the lens is changed from that of a
moderately convex lens to that of a very convex lens.
2) Accommodation of pupils
The pupil constricts when an individual looks at a near object. This is called "Near reflex of
the pupil".
3) Convergence of eye balls
When the eye fixate on a near object, the eyes must converge.
9. Describe the function of the vestibular apparatus.
1) To provide a subjective sensation of movement and/or displacement in 3-dimensional space.
2) To maintain upright body posture (balance).
3) To stabilize the eyes relative to the environment.
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10. What are the differences between scotopic vision system and photopic vision system?
1) Scotopic vision system:
not color sensitive,
mainly more sensitive to light,
peripheral.
2) Photopic vision system:
color sensitive,
less sensitive to light,
mainly fovea.
11. How does the vibration of the basilar membrane encode different frequencies of the sound?
The motion of the basilar membrane is a traveling wave. The base of the basilar membrane
(near the oval window) is three or four times narrower than the apex (the far end of the
cochlea). At the base, the basilar membrane is 100 times stiffer than it is at the apex.
Different frequencies of sound would lead to a different envelope of vibration on the basilar
membrane with a different peak of displacement for each frequency. Therefore, different
frequencies of sound would get a peak vibration in different places on the basilar membrane.
The point of peak vibration of the basilar membrane would presumably cause the most
bending of the cilia and elicit the most response from the hair cells in that part of the cochlea.
High frequencies would cause greatest vibration near the base, and low frequencies would
cause greatest vibrations near the apex.
12. What is the central inhibition? Please describe postsynaptic inhibition and presynaptic
inhibition.
Central inhibition is also called synaptic inhibition which is the inhibition between neurons.
Postsynaptic inhibition:
 Involves direct contact between inhibitory synapse and neuron being inhibited
 Typically involves hyperpolarization- IPSP
 Involves inhibitory inter-neuron
 Types of postsynaptic inhibition: Afferent Collateral Inhibition and recurrent
Inhibition.
Presynaptic inhibition:
 Inhibitory synapse onto presynaptic terminal of excitatory synapse
 Post-synaptic inhibition momentarily reduces ability of cell to respond to excitatory
input
 Presynaptic inhibition reduces amount of neurotransmitter released from an
excitatory terminal
 Works by reducing Ca2+ influx into presynaptic terminal, therefore reducing amount
of neurotransmitter released
13. Please describe the cholinergic fibers and receptors of the body.
The cholinergic fibers:
 Sympathetic and parasympathetic preganglionic fibers
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 Parasympathetic postganglionic fibers
 Motor nerve fibers
 Sympathetic postganglionic fibers to the sweat glands
 Sympathetic vasodilator nerve fibers of the muscles
The cholinergic receptors: M-, N1-, N2-receptor
14. What is the sensory area of cerebral cortex? Please describe its details.
Sensory areas of cerebral cortex
1) Somatosensory cortex
Somatosensory area I: Brodmann’s areas: 3-2-1
Somatosensory area II:
2) Proprioception sensory area (4)
3) Visual cortex
Primary visual cortex (17)
Secondary visual areas (18,19)
4) Auditory cortex (41, 42)
Primary auditory cortex
Secondary auditory areas
15. Describe the regulation of cerebral cortex on somatic movement.
Transmission of signals from the motor cortex to the muscles
1). Pyramidal system (Corticospinal tract)
Pathway: Motor cortex (pyramidal cells)internal capsule forming the pyramids of
the medulla cross to the opposite side in the lower medulla spinal cord (motor
neurons)
Function: It is the direct pathway which concerned more discrete and detailed
movements.
2).Extrapyramidal system
The accessory pathway that involve the basal ganglia, cerebellum, and nuclei of the brain
stem
16. What is the decerebrate rigidity? Please describe the main mechanism of it.
1) Decerebrate rigidity: Extension of the trunk and the four limbs due to impairment to the
mesencephalon. It is accompanied by an irreversible coma and disintegration of vital
signs.
2) Mechanism:
 Blockage of the input to the medullary reticular nuclei from the cerebral cortex, red
nuclei and basal ganglia
 Medullary reticular inhibitor system becomes nonfunctional
 Overactivity of the pontine excitatory system
17. What are visceral activity regulations by hypothalamus?
1). Cardiovascular Regulation
(+)posterior and lateral hypothalamusBPA, HR
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(+)preoptic hypothalamus BPA, HR
2). Regulation of body temperature
PO/AH (the preoptic area)
3). Regulation of body water
Thirst center
Supraoptic nucleus: secrete ADH
4). Regulation of uterine contractility and milk ejection
Paraventricular nucleus: oxytocin
5). Gastrointestinal and feeding regulation
Ventromedial nucleus: satiety center
Lateral hypothalamic area: feeding center
Mammillary bodies: feeding reflexes
6). Hypothalamic control of endocrine hormone secretion by the anterior pituitary gland
7). Behavioral functions
Lateral hypothalamus is involved in controlling rage and fighting
Ventromedial nucleus is involed in satiety, decreased eating, and tranquility
Thin zone of the periventricular nucleus is involved in fear and punishment, sexual
drive
8). Controlling biorhythm
Suprachiasmatic nucleus
18. What are the functions of Wernicke's area, Broca's area, the angular gyrus, and the basal
ganglia in the production of speech?
Wernicke's area: Language comprehension
Broca's area: Controls facial neurons. Controls speech. Understanding language.
The angular gyrus: It is important in the processing of associating a heard name to a seen
or felt object, it is probably also important for associations in the reverse direction.
The basal ganglia: The basal ganglia appear function as a "sequencing engine", allowing
humans to speak and to create new patterns of thought and to create a potentially limitless
number of novel sentences by permuting a finite number of words and syntactic processes.
19. What methods are used to study learning and memory in humans and experimental
animals?
fMRI and PET are usually used for humans for studying learning and memory.
As for experimental animals, hippocampus is the most common brain area for research of
Synaptic plasticity during learning and memory. And the cerebellum is the area for studying
motor memory. The method used for animals is recording the local field potentials in the
above two areas with the presynaptic fibers electrically stimulated and to analyze the
long-term potentiation (LTP) or long-term depression (LTD).
20. How do the brain waves correlate with different stages of sleep?
Slow-wave sleep
1). EEG: Low-frequency, highly synchronized neural activity
Stage 1,2,3,4
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2). Fast-wave sleep
EEG: high-frequency, small amplitude, desynchronized wave
21. Name the hormones secreted by the hypothalamus in humans, and list the main functions of
each.
Name
Releasing Hormone (or Factor)
Thyrotropin releasing hormone (TRH)
Gonadotrpin releasing hormone (GnRH, LHRH)
Corticotropin releasing hormone (CRH)
Growth hormone releasing hormone (GHRH)
Melanocyte stimulating hormone releasing factor (MRF)
Prolactin releasing factor (PRF)
Releasing Inhibiting Hormone
Growth hormone release inhibiting hormone (GHRIH, somatostatin)
Prolactin release inhibiting factor (PIF)
Melanocyte stimulating hormone release inhibiting factor (MIF)
Target Hormone Secretion
TSH
LH,FSH
ACTH
GH
MSH
PRL
GH,TSH, insulin,
glucagons, gastrin
PRL,MSH
MSH
22. What are the mechanisms of action of peptide/protein hormones?
(1) The binding of the hormone to its specific receptor of the target cell
(2) A change in the configuration of the receptor, which becomes activated.
(3) The receptor activation leads through a sequence of reactions to the cell’s
ultimate response to the hormone. The mechanisms of signal transduction involve
three classes key substances in sequence: the G protein, second messengers and
protein kinases. The principle second messengers are cAMP, IP3, DG and Ca2+.
23. List the main physiological actions of thyroid hormones.
(1) Effects of thyroid hormone on general metabolism
Thyroid hormone exerts numerous effects on metabolic processes in a wide variety of
different tissues and cells.
 Calorigenesis or the heat production and BMR in the body
 Glucose absorption from the intestine and increase the uptake of glucose from the blood
into adipose tissue and muscle
All aspects of lipids. In general, however, the degradation is affected more than synthesis.
 Protein synthesis when present in physiological concentrations. However, when the
thyroid hormone is present in excess, it tends to cause a decrease in protein synthesis and an
increase in protein breakdown.
 Cardiac output by increasing both the rate and the strength of cardiac contraction.
Systolic blood pressure is augmented and diastolic blood pressure is decreased , so that the
net result is a widened pulse pressure.
(3) Effects of The Thyroid Hormone on Growth and Development
The thyroid hormone is required for normal skeletal growth. Development and maturation
(2)
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of the central nervous system are markedly affected by thyroid hormones.
24. What are the endocrinologic causes of dwarfism and cretinism, and how does each lead to
short stature?
Dwarfism can be duo to GRH deficiency, growth hormone deficiency, deficient secretion
of IGF-I, or other causes in childhood.
Cretinism can be due to deficiency of thyroid hormone during the period of fetal and early
neonatal development.
Short stature is the result of the disproportionate growth of the skeleton. Growth hormone
and thyroid hormones are required for normal skeletal growth. They can regulate the growth of
bone.
25. Describe the functions of cortisol and the mechanisms that regulate secretion of
glucocorticoids.
Functions of cortisol:
(1) Effect on metabolism
 Blood glucose concentration by stimulating gluconeogenosis by the liver and  the rate
of glucose utilization by the cells.
 Protein store in extrahepatic tissues by  protein synthesis and  catabolism of protein
already in the cells.
 Mobilization of fatty acids from adipose tissue and  oxidation of fatty acids
The patients with excess cortisol secretion develop a peculiar type of obesity with excess
deposition of fat in the abdomen, trunk and face, giving a buffalo-like torso and rounded face, a
“moon face”.
(2) Effect of cortisol in stress
Cortisol is resistant to stress.
(3) Effect of glucoticoids on some organs and tissues
Vascular System. Cortisol permits normal responsiveness of arterioles to the constrictive
action of catecholamines by decreasing the degradation of catecholamines. Cortisol is required
for the maintenance of normal blood pressure.
Blood cells.  The number of red blood cells, platelet, and neutrophils and  the number of
eosinophils and lymphocytes in the blood.
Central Nervous System. The brain possesses receptors for adrenal glucocorticoids.
Regulation of glucocorticoids secretion:
The glucocorticoid secretion is regulated by feedback mechanisms.
CRH:  ACTH synthesis and secretion
ACTH:  Glucocorticoid (cortisol) synthesis and secretion, inhibits the release of CRH
through a short-loop feedback
Cortisol: inhibits pituitary ACTH synthesis and secretion through negative (long-loop)
feedback. Cortisol also has direct negative feedback effects on the hypothalamus to derease the
formation of CRH.
All these feedbacks help regulate the plasma concentration of cortisol.
26. Describe the effects of insulin.
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(1) Effects of insulin on carbohydrate metabolism
The insulin causes rapid uptake, storage, and use of glucose by almost all tissue of the
body especially by liver, muscle, and adipose tissue.
(2) Effect of insulin on fat metabolism.
Insulin rapidly lower the circulating levels of free fatty acids and ketoacids and may
eventually decrease the level of triglycerides. The net effect of insulin on fat metabolism is to
increase storage and to block mobilization and oxidation of fatty acids.
(3) Effect of insulin on protein metabolism and on growth
Insulin increases protein synthesis, especially the enzymes for storage of carbohydrates,
fats and proteins. Insulin inhibits the catabolism of proteins. It is equally as essential for growth
of an animal as is growth hormone.
27. What are the disadvantages of long-term, high dose treatment with glucocorticoids in diseases
such as rheumatoid arthritis and asthma? What problems occur when steroid treatment is
stopped suddenly?
Long-term, high dose treatment with glucocorticoids the degree of pituitary
inhibitionACTH secretion adrenal insufficiency steroid treatment is stopped
suddenly Lack of glucocorticoids
28. Describe the roles of the pituitary and the hypothalamus in the regulation of ovarian function,
and the role of feedback loops in this process.
The hypothalamic-pituitary-ovarian (HPO) axis
GnRH:  synthesis and release of FSH and LH
FSH: stimulating the ovarian follicles to develop and to secrete estradiol
LH: luteotrophic, progesterone production by the corpus luteum
Estrogen and progesterone exert negative feedback effect on the hypothalamus and the
anterior pituitory to decrease GnRH and gonadotropin release via long feedback loop.
Gonadotropins may inhibit the secretion of GnRH (via short feedback loop)
GnRH may exert an inhibitory effect on its own secretion (via ultra short feedback loop)
The preovulatory rise in estrogen may exert positive feedback effect on the hypothalamus to
increase GnRH release. The positive feedback effect of the preovulatory rise in estrogens is also
augmented by the small increase in progesterone that occurs around the time of the gonadotropin
surge (before ovulation).
Inhibin also plays a significant role in the feedback regulation of gonadotropin secretion.
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