Download Nerve activates contraction

The Endocrine System
•Second controlling system of the body
•Nervous system is the fast-control system
•Uses chemical messengers (hormones) that
are released into the blood
•Hormones control several major processes
•Reproduction
•Growth and development
•Mobilization of body defenses
•Maintenance of much of homeostasis
•Regulation of metabolism
Hormone Overview
•Hormones are produced by specialized cells
•Cells secrete hormones into extracellular fluids
•Blood transfers hormones to target sites
•These hormones regulate the activity of other
cells
The Chemistry of Hormones
•Hormones are classified chemically as
•Amino acid–based, which includes
•Proteins
•Peptides
•Amines
•Steroids—made from cholesterol
•Prostaglandins—made from highly active lipids
Mechanisms of Hormone Action
•Hormones affect only certain tissues or organs
(target cells or target organs)
•Target cells must have specific protein
receptors
•Hormone-binding alters cellular activity
Effects Caused by Hormones
•Changes in plasma membrane permeability or
electrical state
•Synthesis of proteins, such as enzymes
•Activation or inactivation of enzymes
•Stimulation of mitosis
•Promotion of secretory activity
The Chemistry of Hormones
•Two mechanisms in which hormones act
•Direct gene activation
•Second-messenger system
Direct Gene Activation (Steroid Hormone
Action)
•Diffuse through the plasma membrane of
target cells
•Enter the nucleus
•Bind to a specific protein within the nucleus
•Bind to specific sites on the cell’s DNA
•Activate genes that result in synthesis of new
proteins
Steroid
hormone
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormonereceptor complex
4
DNA
mRNA
5
New
protein
Plasma
membrane
of target
cell
6
(a) Steroid hormone action
Figure 9.1a
Steroid
hormone
Cytoplasm
Nucleus
1
Figure 9.1a, step 1
Steroid
hormone
Nucleus
Cytoplasm
1
2
Receptor
protein
Figure 9.1a, step 2
Steroid
hormone
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormonereceptor complex
Figure 9.1a, step 3
Steroid
hormone
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormonereceptor complex
4
DNA
Figure 9.1a, step 4
Steroid
hormone
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormonereceptor complex
4
DNA
mRNA
5
Figure 9.1a, step 5
Steroid
hormone
Nucleus
Cytoplasm
1
Receptor
protein
2
3
Hormonereceptor complex
4
DNA
mRNA
5
New
protein
Plasma
membrane
of target
cell
6
Figure 9.1a, step 6
Second-Messenger System (Nonsteroid
Hormone Action)
•Hormone binds to a membrane receptor
•Hormone does not enter the cell
•Sets off a series of reactions that activates an
enzyme
•Catalyzes a reaction that produces a secondmessenger molecule (such as cAMP)
•Oversees additional intracellular changes to
promote a specific response
Cytoplasm
Nonsteroid
hormone (first
messenger)
Enzyme
ATP
3
1
2
Receptor
protein
Plasma
membrane
of target cell
Second
cAMP messenger
4
Effect on cellular function,
such as glycogen
breakdown
(b) Nonsteroid hormone action
Figure 9.1b
Nonsteroid
hormone (first
messenger)
Cytoplasm
1
Receptor
protein
Figure 9.1b, step 1
Nonsteroid
hormone (first
messenger)
Cytoplasm
Enzyme
1
2
Receptor
protein
Figure 9.1b, step 2
Cytoplasm
Nonsteroid
hormone (first
messenger)
Enzyme
ATP
3
1
2
Second
cAMP messenger
Receptor
protein
Figure 9.1b, step 3
Cytoplasm
Nonsteroid
hormone (first
messenger)
Enzyme
ATP
3
1
2
Receptor
protein
Plasma
membrane
of target cell
Second
cAMP messenger
4
Effect on cellular function,
such as glycogen
breakdown
Figure 9.1b, step 4
Control of Hormone Release
•Hormone levels in the blood are mostly
maintained by negative feedback
•A stimulus or low hormone levels in the blood
triggers the release of more hormone
•Hormone release stops once an appropriate
level in the blood is reached like insulin &
thyroid hormones
Hormonal Stimuli of Endocrine Glands
•Most common stimuli
•Endocrine glands are activated by other
hormones
•Examples:
•Anterior pituitary hormones travel to target
glands, such as the thyroid gland, to prompt the
release of a particular hormone, such as thyroid
hormone
(a) Hormonal stimulus
1 The hypothalamus secretes
hormones that…
Hypothalamus
2 …stimulate
the anterior
pituitary
gland to
secrete
hormones
that…
Thyroid
gland
Anterior
pituitary
gland
Adrenal
cortex
Gonad
(Testis)
3 …stimulate other endocrine
glands to secrete hormones
Figure 9.2a
Humoral Stimuli of Endocrine Glands
•Changing blood levels of certain ions stimulate
hormone release
•Humoral indicates various body fluids such as
blood and bile
•Examples:
•Parathyroid hormone and calcitonin are
produced in response to changing levels of
blood calcium levels
•Insulin is produced in response to changing
levels of blood glucose levels
(b) Humoral stimulus
1 Capillary blood contains low
concentration of Ca2+, which
stimulates…
Capillary
(low Ca2+
in blood)
Parathyroid
glands
Thyroid gland
(posterior view)
Parathyroid
PTH glands
2 …secretion of parathyroid
hormone (PTH) by parathyroid
glands
Figure 9.2b
Neural Stimuli of Endocrine Glands
•Nerve impulses stimulate hormone release
•Most are under the control of the sympathetic
nervous system
•Examples:
•The release of norepinephrine and epinephrine
by the adrenal medulla
(c) Neural stimulus
1 Preganglionic sympathetic
fiber stimulates adrenal medulla
cells…
CNS (spinal cord)
Preganglionic
sympathetic fibers
Medulla of
adrenal
gland
Capillary
2 …to secrete catecholamines
(epinephrine and norepinephrine)
Figure 9.2c
Major Endocrine Organs
•Pituitary gland
•Thyroid gland
•Parathyroid glands
•Adrenal glands
•Pineal gland
•Thymus gland
•Pancreas
•Gonads (Ovaries and Testes)
•Hypothalamus
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Figure 9.3
Pituitary Gland
•Size of a pea
•Hangs by a stalk from the hypothalamus in the
brain
•Protected by the sphenoid bone
•Has two functional lobes
•Anterior pituitary—glandular
tissue(adenohypophysis.)
•Posterior pituitary—nervous
tissue(neurohypophysis)
•Often called the “master endocrine gland”
Hormones of the Anterior Pituitary
•Six anterior pituitary hormones
•Two affect non-endocrine targets
•Growth hormone
•Prolactin
•Four stimulate other endocrine glands (tropic
hormones)
•Thyroid-stimulating hormone (thyrotropic
hormone)TSH
•Adrenocorticotropic hormone(ACTH)
•Two gonadotropic hormones(FSH, LH)
Hormones of the Anterior Pituitary
•Characteristics of all anterior pituitary
hormones
•Proteins (or peptides)
•Act through second-messenger systems
•Regulated by hormonal stimuli, mostly
negative feedback
Releasing hormones
secreted into portal
circulation
Hypothalamus
Anterior pituitary
Posterior pituitary
Hypophyseal
portal system
Adrenocorticotropic
hormone (ACTH)
Growth hormone (GH)
Bones and muscles
Prolactin (PRL) Follicle-stimulating
hormone (FSH)
and luteinizing
Mammary
hormone (LH)
glands
Thyrotropic
hormone (TH)
Adrenal cortex
Thyroid
Testes or ovaries
Figure 9.4
Hormones of the Anterior Pituitary
•Growth hormone
•General metabolic hormone
•Major effects are directed to growth of skeletal
muscles and long bones
•Plays a role in determining final body size
•Causes amino acids to be built into proteins
•Causes fats to be broken down for a source of
energy
Hormones of the Anterior Pituitary
•Growth hormone (GH) disorders
•Pituitary dwarfism results from hyposecretion
of GH during childhood
•Gigantism results from hypersecretion of GH
during childhood
•Acromegaly results from hypersecretion of GH
during adulthood
Pituitary dwarf (left), Giant (center), Normal height woman (right)
Figure 9.5
Hormones of the Anterior Pituitary
•Prolactin (PRL)
•Stimulates and maintains milk production
following childbirth by increasing # of milk ducts
& milk glands, no realse of milk
•Adrenocorticotropic hormone (ACTH)
•Regulates endocrine activity of the adrenal
cortex
•Thyroid-stimulating hormone (TSH)
•Influences growth and activity of the thyroid
gland
Hormones of the Anterior Pituitary
•Gonadotropic hormones
•Regulate hormonal activity of the gonads
•Follicle-stimulating hormone (FSH)
•Stimulates follicle development in ovaries, the
grafian follicle that secretes estrogen
•Stimulates sperm development in testes
•Luteinizing hormone (LH)
•Triggers ovulation of an egg in females, it acts
on the corpus lutium to secrete progestron
•Stimulates testosterone production in males
Pituitary–Hypothalamus Relationship
•Hormonal release is regulated by releasing
and inhibiting hormones produced by the
hypothalamus
•Hypothalamus produces two hormones
•These hormones are transported to
neurosecretory cells of the posterior pituitary
•Oxytocin
•Antidiuretic hormone
•The posterior pituitary is not strictly an
endocrine gland, but does release hormones
Hormones of the Posterior Pituitary
•Oxytocin
•Stimulates contractions of the uterus during
labour, sexual relations, and breastfeeding
•Causes milk ejection in a nursing woman after
suckling
Hormones of the Posterior Pituitary
•Antidiuretic hormone (ADH)
•Inhibits urine production by promoting water
reabsorption by the kidneys
•In large amounts, causes vasoconstriction
leading to increased blood pressure
•Also known as vasopressin
Hypothalamic
neurosecretory
cells
Hypothalamus
Optic
chiasma
Axon
terminals
Arterial blood supply
Posterior lobe
Capillary bed
Venous drainage
Anterior lobe
of the pituitary
ADH
Oxytocin
Kidney tubules
Mammary glands
Uterine muscles
Figure 9.6
Thyroid Gland
•Found at the base of the throat
•Consists of two lobes and a connecting
isthmus
•Produces two hormones
•Thyroid hormone
•Calcitonin
Thyroid cartilage
Epiglottis
Common carotid
artery
Isthmus of
thyroid gland
Trachea
Brachiocephalic
artery
Left subclavian
artery
Left lobe of
thyroid gland
Aorta
(a) Gross anatomy of the thyroid gland, anterior view
Figure 9.7a
Thyroid Gland
•Thyroid hormone
•Major metabolic hormone
•Composed of two active iodine-containing
hormones
•Thyroxine (T4)—secreted by thyroid follicles
•Triiodothyronine (T3)—conversion of T4 at
target tissues
Colloid-filled
Follicle cells
follicles
Parafollicular cell
(b) Photomicrograph of thyroid gland
follicles (125×)
Figure 9.7b
Thyroid Gland
•Thyroid hormone disorders
•Goiters
•Thyroid gland enlarges due to lack of iodine
•Salt is iodized to prevent goiters
•Types:simple nodular, toxic(Graves disease) &
malignant
•Cretinism
•Caused by hyposecretion of thyroxine during
childhood
Figure 9.8
Thyroid Gland
•Thyroid hormone disorders (continued)
•Myxedema
•Caused by hypothyroidism in adults
•Results in physical and mental slugishness
with rapid increase in weight
•Graves’ disease( toxic goiter)
•Caused by hyperthyroidism
•Results in increased metabolism, heat
intolerance, rapid heartbeat, weight loss, and
exophthalmos
Figure 9.9
Thyroid Gland
•Calcitonin
•Decreases blood calcium levels by causing its
deposition on bone
•Antagonistic to parathyroid hormone
•Produced by parafollicular cells
•Parafollicular cells are found between the
follicles
Colloid-filled
Follicle cells
follicles
Parafollicular cell
(b) Photomicrograph of thyroid gland
follicles (125×)
Figure 9.7b
Parathyroid Glands
•Tiny masses on the posterior of the thyroid
•Secrete parathyroid hormone (PTH)
•Stimulate osteoclasts to remove calcium from
bone
•Stimulate the kidneys and intestine to absorb
more calcium
•Raise calcium levels in the blood
Calcitonin
Calcitonin
stimulates
calcium salt
deposit in bone.
Thyroid gland
releases calcitonin.
Stimulus
Rising blood
Ca2+ levels
Calcium homeostasis of blood: 9–11 mg/100 ml
BALANCE
BALANCE
Stimulus
Falling blood
Ca2+ levels
Thyroid
gland
Osteoclasts
degrade bone
matrix and
release Ca2+
into blood.
Parathyroid
glands
PTH
Parathyroid
glands release
parathyroid
hormone (PTH).
Figure 9.10
Adrenal Glands
•Sit on top of the kidneys
•Two regions
•Adrenal cortex—outer glandular region has
three layers
•Mineralocorticoids secreted by outermost
layer(zona glumerulosa)
•Glucocorticoids secreted by middle layer(z.
faciculata)
•Sex hormones secreted by innermost layer(z.
reticularis)
Adrenal
gland
Kidney
Capsule
Mineralocorticoidsecreting area
Glucocorticoidsecreting area
Adrenal
cortex
Adrenal gland
• Medulla
• Cortex
Kidney
Sex hormone
secreting area
Adrenal
medulla
Figure 9.11
Hormones of the Adrenal Cortex
•Mineralocorticoids (mainly aldosterone)
•Produced in outer adrenal cortex
•Regulate mineral content in blood
•Regulate water and electrolyte balance, it
keeps Na &release K
•Target organ is the kidney
•Production stimulated by renin
•Production inhibited by atrial natriuretic
hormon (ANH)
Decreased Na+ or
increased K+ in
blood
Stress
Hypothalamus
Decreased
blood volume
and/or blood
pressure
Corticotropinreleasing hormone
Anterior pituitary
Increased
ACTH blood pressure
or blood volume
Kidney
Renin
Indirect
stimulating
effect via
angiotensin
Angiotensin II
Direct
stimulating
effect
Heart
Atrial natriuretic
peptide (ANP)
Inhibitory
effect
Mineralocorticoidproducing part of
adrenal cortex
Enhanced secretion
of aldosterone targets
kidney tubules
Increased absorption
of Na+ and water;
increased K+ excretion
Increased blood
volume and
blood pressure
Figure 9.12
Hormones of the Adrenal Cortex
•Glucocorticoids (including cortisone and
cortisol)
•Produced in the middle layer of the adrenal
cortex
•Promote normal cell metabolism(antiinflammatory)& antiallergic
•Help resist long-term stressors(antidepressant)
•Released in response to increased blood
levels of ACTH
Short term
More prolonged
Stress
Hypothalamus
Releasing hormones
Nerve impulses
Spinal cord
Corticotropic cells of
anterior pituitary
ACTH
Preganglionic
Adrenal sympathetic
medulla fibers
Mineralocorticoids
Short-term stress response
Catecholamines
(epinephrine and
norepinephrine)
1. Increased heart rate
2. Increased blood pressure
3. Liver converts glycogen
to glucose and releases
glucose to blood
4. Dilation of bronchioles
5. Changes in blood flow
patterns, leading to
increased alertness and
decreased digestive and
kidney activity
6. Increased metabolic rate
Adrenal
cortex
Glucocorticoids
Long-term stress response
1. Retention of sodium
and water by kidneys
2. Increased blood
volume and blood
pressure
1. Proteins and fats
converted to
glucose or broken
down for energy
2. Increased blood
sugar
3. Suppression of
immune system
Figure 9.13
Hormones of the Adrenal Cortex
•Sex hormones
•Produced in the inner layer of the adrenal
cortex
•Small amounts are made throughout life
•Mostly androgens (male sex hormones) are
made but some estrogens (female sex
hormones) are also formed
Adrenal Glands
•Adrenal cortex disorders
•Addison’s disease
•Results from hyposecretion of all adrenal cortex
hormones
•Bronze skin tone, muscles are weak, burnout,
susceptibility to infection
•Hyperaldosteronism
•May result from an ACTH-releasing tumor
•Excess water and sodium are retained leading to
high blood pressure and edema
Adrenal Glands
•Adrenal cortex disorders
•Cushing’s syndrome
•Results from a tumor in the middle cortical area of
the adrenal cortex
•“Moon face,” “buffalo hump” on the upper back,
high blood pressure, hyperglycemia, weakening of
bones, depression
•Masculinization
•Results from hypersecretion of sex hormones
•Beard and male distribution of hair growth
Hormones of the Adrenal Medulla
•Produces two similar hormones
(catecholamines)
•Epinephrine (adrenaline)
•Norepinephrine (noradrenaline)
•These hormones prepare the body to deal with
short-term stress (“fight or flight”) by
•Increasing heart rate, blood pressure, blood
glucose levels
•Dilating small passageways of lungs
Adrenal
gland
Kidney
Capsule
Mineralocorticoidsecreting area
Glucocorticoidsecreting area
Adrenal
cortex
Adrenal gland
• Medulla
• Cortex
Kidney
Sex hormone
secreting area
Adrenal
medulla
Figure 9.11
Pancreatic Islets
•The pancreas is a mixed gland and has both
endocrine and exocrine functions
•The pancreatic islets produce hormones
•Insulin—allows glucose to cross plasma
membranes into cells from beta cells
•Glucagon—allows glucose to enter the blood
from alpha cells
•These hormones are antagonists that maintain
blood sugar homeostasis
Stomach
Pancreas
(a)
Figure 9.14a
Exocrine
cells of
pancreas
Pancreatic
islets
(b)
Figure 9.14b
Exocrine
cells of
pancreas
Alpha (α)
cells
Capillaries
Cord of beta (β) cells secreting
insulin into capillaries
(c)
Figure 9.14c
Uptake of glucose
from blood is
enhanced in most
body cells
Insulin-secreting cells
of the pancreas
activated; release
insulin into the blood
Insulin
Tissue cells
Glucose Glycogen
Pancreas
Elevated blood
sugar level
Liver takes up
glucose and stores
as glycogen
Stimulus
Blood
glucose level
(e.g., after
eating four
jelly doughnuts)
Stimulus
Blood glucose
level (e.g., after
skipping a meal)
Blood glucose rises
to homeostatic
set point; stimulus
for glucagon
release diminishes
Liver breaks
down glycogen
stores and
releases
glucose to the
blood
Blood glucose
falls to homeostatic
set point; stimulus
for insulin release
diminishes
Low blood sugar level
Glucagon-releasing
cells of pancreas
activated; release
glucagon into blood
Glucose Glycogen
Liver
Glucagon
Figure 9.15
Pineal Gland
•Found on the third ventricle of the brain
•Secretes melatonin
•Helps establish the body’s wake and sleep
cycles
•Believed to coordinate the hormones of fertility
in humans
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Figure 9.3
Thymus Gland
•Located posterior to the sternum
•Largest in infants and children
•Produces thymosin
•Matures some types of white blood cells
•Important in developing the immune system
Gonads
•Ovaries
•Produce eggs
•Produce two groups of steroid hormone
•Estrogens
•Progesterone
•Testes
•Produce sperm
•Produce androgens, such as testosterone
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
Figure 9.3
Hormones of the Ovaries
•Estrogens
•Stimulate the development of secondary
female characteristics
•Mature female reproductive organs
•With progesterone, estrogens also
•Promote breast development
•Regulate menstrual cycle
Hormones of the Ovaries
•Progesterone
•Acts with estrogen to bring about the
menstrual cycle
•Helps in the implantation of an embryo in the
uterus
•Helps prepare breasts for lactation
Hormones of the Testes
•Produce several androgens
•Testosterone is the most important androgen
•Responsible for adult male secondary sex
characteristics
•Promotes growth and maturation of male
reproductive system
•Required for sperm cell production
Other Hormone-Producing Tissues and
Organs
•Parts of the small intestine
•Parts of the stomach
•Kidneys
•Heart
•Many other areas have scattered endocrine
cells
Endocrine Function of the Placenta
•Produces hormones that maintain the
pregnancy
•Some hormones play a part in the delivery of
the baby
•Produces human chorionic gonadotropin
(hCG) in addition to estrogen, progesterone,
and other hormones
Developmental Aspects of the Endocrine
System
•Most endocrine organs operate smoothly until
old age
•Menopause is brought about by lack of
efficiency of the ovaries
•Problems associated with reduced estrogen
are common
•Growth hormone production declines with age
•Many endocrine glands decrease output with
age