Lecture #17: The Vertebrate Endocrine System (Fig. 45.5)
I. THE
HYPOTHALAMUS AND PITUITARY GLAND
A. GENERAL
FEATURES OF THE HYPOTHALAMUS (Fig.
45.6a)
1. It functions
to integrate the nervous and endocrine systems.
2. It possesses
hormone-releasing nerve cells called neurosecretory cells.
3. Neurosecretory
cells secrete hormone-like peptides called releasing factors.
4. There are two
main sets of neurosecretory cells in the hypothalamus:
a. one set
controls the anterior pituitary gland.
b. the other set
controls (and comprises) the posterior pituitary gland.
B. HYPOTHALAMUS
AND POSTERIOR PITUITARY(neurohypophysis)
(Fig. 45.6a)
1. The posterior
pituitary consists of modified nerve cells.
a. ADH (a
nonapeptide) acts on kidneys to increase Na+ and H20
retention.
b. Oxytocin
(a related nonapeptide) acts on:
(1) mammary
glands to eject milk.
(2) myometrium of
the uterus to promote parturition.
C. HYPOTHALAMUS
AND ANTERIOR PITUITARY (adenohypophysis)
(Fig. 45.6b)
1. Anterior
pituitary arises from epithelial cells in the roof of the mouth.
2. Hypothalamic
neurosecretory cells terminate on capillaries in median eminence.
3. Portal
veins carry releasing factors to endocrine cells of anterior pituitary.
4. Releasing
factors regulate the secretions from the anterior pituitary.
II. HORMONAL
SECRETIONS OF THE ANTERIOR PITUITARY (Fig. 45.6b)
(NOTE: Anterior Pituitary hormones regulate growth and homeostasis.)
1. Growth
hormone affects a wide variety of tissues. (somatomedins from the
liver)
2. Prolactin
is similar to GH in structure, and influences many tissues.
3. FSH and LH
are closely related gonadotropins which stimulate steroid secretions.
4. TSH
(also a glycoprotein) stimulates the thyroids to produce T3
and T4.
5. Pro-opiomelanocortin:
(Fig. X)
a. adrenocorticotropin
(ACTH) stimulates adrenal steroid synthesis.
b. melanocyte-stimulating
hormone (MSH) stimulates pigment-containing cells.
c. endorphins
and enkephalins are the body's natural pain killers.
III. OTHER
GLANDULAR TISSUES
1. T3
and T4 are tyrosine derived, lipid soluble,
calorigenics. (Figs. 45.7 & 45.8)
2. Parathyroids
(PTH and Calcitonin) increase and decrease Ca++,
respectively. (Fig. 45.9)
3. Pancreas
(islet cells). (Fig. 45.10)
a. a-cells
produce glucagon to increase blood sugar.
b. ß-cells
produce insulin to decrease blood sugar.
4. Adrenal
glands: (Fig. 45.14)
a. adrenal
medulla and the short-term stress response. (epi & norepi) (Fig. 45.11)
(1) the synthesis
of catecholamine hormones (Fig. 45.12).
b. adrenal
cortex and the long-term stress response: (Fig.
45.14 & 45.13a)
(1) the
glucocorticoid cortisol promotes glucose formation from proteins.
(2) the
mineralocorticoid aldosterone reabsorbs H2O and raises blood
pressure.
5. Gonads
(steroids) (Fig. 45.13b)
6. Pineal
(melatonin)
7. Thymus
(thymosin)