Download Biology 202 Lecture Notes

Biology 202 Lecture Notes
Chapter 15 The Endocrine System
Objectives:
1. Indicate important differences between hormonal and neural controls of body functioning.
2. Describe how hormones are classified chemically.
3. Describe the two major mechanisms by which hormones bring about their effects on their target
tissues, and explain how hormone release is regulated.
4. Describe the structural and functional relationships between the hypothalamus and the pituitary
gland.
5. List and describe the chief effects of adenohypophysis hormones
6. Discuss the structure of neurohypophysis, and describe the effects of the two hormones.
7. Describe the important effects of the two groups of hormones produced by the thyroid gland.
Follow the process of thyroxine release.
8. Indicate the general functions of parathyroid hormone.
9. List the hormones produced by the adrenal gland, and cite their physiological effects.
10. Compare and contrast the effects of the two major pancreatic hormones.
11. Describe the functional roles of hormones of the testes and ovaries.
12. Name a hormone produced by the heart, and localize enteroendocrine cells.
13. Briefly explain the hormonal functions of placenta, kidney, skin, and adipose tissue.
Hormonal vs. neural controls

Both are systems that regulate the functions of the body. Neural are almost instantaneous, shortlived and use cells to transmit impulses. Hormonal are delayed, longer-lasting, and use chemicals
called HORMONES to influence metabolic activities.

The endocrine system is the 2nd messenger system of the body and does interact with the nervous
system.

Products of endocrine glands are released directly into the bloodstream, while those of exocrine
glands are released through ducts.
Processes influenced or controlled
1.
Reproduction
2.
Growth and development
3.
Mobilizing body defenses against stressors
4.
Maintaining electrolyte, fluid, and nutrient balance in blood
5.
Regulating cellular metabolism and energy balance
Types of Hormones

Amino-acid based (polypeptide or protein)

Steroids (lipid): cholesterol is their precursor
Mechanisms of Hormone Action: target cell activity is altered by hormones (up or down). Response
depends on target cell type.
1.
Alters membrane permeability or membrane potential (electrical state) or both by opening or
closing ion channels.
2.
Stimulates the synthesis of proteins or certain regulatory molecules (such as enzymes) within cell
(tropic hormone)
3.
Activates or deactivates enzymes.
4.
Induces secretory activity (tropic hormone)
5.
Stimulates mitosis
Second Messenger System: found in target cells. Necessary when protein or peptide hormones are too
large (or polar) to penetrate cell membrane of target cell.
1. cAMP: G protein is found in cell membrane and is activated when hormone binds to its receptor.
This stimulates or inhibits the production of cAMP in target cell which in turn stimulates or inhibits
reactions within cell. See figure 15.2
2. PIP Calcium: G protein is stimulated again, but this time activates PIP which causes the release of
calcium from the SER. Calcium (Ca2+) then activates other enzymes in cell. See figure 15.3
Gene Activation: steroid hormones pass through cell membrane (as well as thyroid hormone), bind to
intracellular receptor and they both go to nuclear chromatin. See figure 15.4

The hormone then binds to DNA to turn on gene that then prompts translation of gene product
(enzymes, structural proteins) that promotes metabolism or is exported.
Insulin and other growth factors: there are no 2nd messengers in the target cells for insulin and other
growth factors.
Hormone-target cell specificity: receptors present on target cells are for specific hormones
1. Receptors (#’s may vary)
 Rising blood levels of hormone may cause more receptors on target cell in up regulation ( to
increase responsiveness of target cells)

Rising blood levels may cause a decrease in receptor number in down regulation (to keep
target cells from overreacting
2. Affinity
 The attraction or likelihood and strength of bond between the hormone and the receptors
on the target cells.
Interaction of Hormones at Target Cells
 Permissiveness: one hormone cannot exert its full effects without another hormone being present.
 Synergism: more than one hormone produces the same effects at the target cell and their
combined effects are amplified.
 Antagonism: one hormone opposes the action of another hormone.
Control of hormone release See figure 15.5
Negative vs. positive feedback
 In negative feedback, as plasma levels of hormone increase, the gland is inhibited from
more production of the hormone, by the hormone itself (insulin or glucagon).
 In positive feedback, as plasma levels of hormone increase, the gland is stimulated to
produce more of the same hormone and more hormone release.
1. Humoral stimuli
 The gland is affected by changing blood levels of ions or nutrients (ex. insulin, glucagon,
aldosterone)
2. Neural stimuli
 Sympathetic stimulus in the adrenal medulla by the hypothalamus causes the release of
epinephrine and norepinephrine
3. Hormonal stimuli
 The gland is stimulated or inhibited by other hormones (releasing or inhibiting
hormones)
Hypothalamus and Pituitary gland See figure 15.6
 The hypothalamus is connected to the pituitary gland by the infundibulum.
 Hypothalamic neurons go directly to the posterior pituitary (neurohypophysis) and
release oxytocin and ADH (antidiuretic hormone or vasopressin)
 Releasing and inhibiting hormones pass through the hypophyseal portal system of
capillaries to influence the anterior pituitary gland (adenohypophysis)
See Table 15.1