A&P II- Chap 1

The Endocrine System:

*Hormone: a chemical messenger (secreted by an endocrine gland) that enters the blood stream & travels to it’s “target cells” to have an effect

Endocrine system: longterm regulation (nervous system → short term regulation)

Major endocrine glands: 

-pituitary, thyroid, parathyroids, adrenals, pineal 

Other hormone secreting glands: 

Hypothamlamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, heart, adipose tissue, placenta. 

Hormone receptors*- are proteins on or in the target cells. They bind a particular hormone (particular). 

$Paracrines: hormones that act on neighboring cells.

@Autocrines: hormones that act on small cells that secreted it. 

ex . $: nitric oxide: secreted by endothelial cells in vessels→ act on smooth muscle in walls of vessels→ vasodilation. 

Ex. @: Interlukin-2 (IL-2)---> secreted by the helper t-cells. Effects the t-cell itself and other immune cells. 

Chemical classes of hormones: 

1. Lipid soluble hormones: 

a. Steroids- derived from cholestrol

B. thyroid hormones

C. nitric oxide: both hormones and neurotransmitter 

2. Water soluble hormones: “peptide hormones” amino acid based hormones.

1. Amine hormones: modified amino acids

2. Peptide hormones: larger, longer chains of amino acids

3. Eciosaniods: derived from fatty acids ex. Prostaglands, leukotrines.

*Most water soluble hormones travel freely in blood plasma

*Most lipid soluble hormon es use “plasma protein” transporters from liver to travel blood plasma. 

3 functions of transporter proteins: 

1. Temporarily make lipid soluble hormones water soluble

2. Provide a stage of hormone in the blood.

3. Prevent lipid soluble hormones from crossing filtration membrane in the kidney. 

Hormone action mechanisms: (what hormones do when they reach their target site.)

1. Synthesis of a new molecule 

2. Change target cell permeability

3. Transporter molecules into/out of a target cell

4. Regulate metabolism of target cell. 

5. Cause contraction of cardiac or smooth muscle. 

Hormone/recpetor interaction: 

*Lipid soluble hormones

-bind to receptor inside target cell

-hormone binds receptor in cytoplasm or in nucleus 

- hormone/receptor complex regulates gene expression in nucleus 

-if gene turned “on” DNA—>mRNA—> ribosome—> translation—> protein! (synthesis)

- New protein alters target cell’s activity. 

Continued: Hormone/receptor interactions 

Review**: Lipid Soluble hormones 

-Pass through target cell membrane (because theyre lipid soluble).

-Hormone binds to receptor in cytoplasm or in nucleus 

- hormone/receptor complex enters nucleus and regulates gene expression (on or off)

-If turned on, DNA→mRNA—>ribosome—> translation—-> protein synthesis 

New*: Water soluble hormones (a.a, peptide, eicosanoids)

-Hormone cannot cross target cell’s plasma membrane 

-Hormone must bind to a surface receptor on target cell plasma membrane

-Hormone is called the “1st messenger” 

- When hormone binds to surface receptor, complex activates a G-protein inside target cell —> activates adenylate cyclase (enzyme)-----> converts ATP to cAMP (2nd messenger).

-cAMP activates protein kinases—> phosphorylation of proteins—--> *regulates cellular metabolism.

Hormone interactions: 3 determining factors of responsiveness of hormone @target cell: 

1. Hormone blood contraction 

2. Number of target cell’s receptors

3. Influence of other hormones 

Permissive effect: WHen 1 hormone requires the effect of another hormone in order to have an effect. The presence of thyroid hormone at a cell greatly enhances the effect of epinephrine at that cell.

Synergistic effect: When hormones together have a greater effect @target cell than each hormone individually. Ex: afch and estrogen on oocyle development. 

Antagonistic effect: When 1 hormone opposes the effect of another ex. Insulin and glycogen 

Hormone secretion regulation: 

1. Nervous system

2. Chemical changes in blood 

3. Other hormones

*most regulate mechanisms work via negative feedback

Endocrine glands and their hormones: 

Hypothamlamus: the major endocrine gland (in brain) that secretes 9 “releasing hormones” —> “inhibiting hormones” 

Hormones released by the anterior pituitary:

1. Human growth hormone (hGH)- stimulates liver, skeletal muscle, bones to secrete IGF’s (insulin like growth factors) *during adolescence. 

2. Thyroid stimulating hormones (TSH): target: thyroid effect: stimulates thyroid to secrete T3 T4 

3. Follicle stimulating hormone(FSH): target: ovaries, testes

 effect: women- increases follicular development and estrogen secretion. 

Males: increases sperm production 

4. Luteinzing hormones: target: ovaries, testes 

Effect: females: triggers ovulation

Males: testosterone secretion

5. Prolactin (PRL) target: women breasts effect: stimulates milk production in pregnant mother 

6. Adrenocorticotropic hormone (ACTH): 

Target: adrenal cortex 

Effect: help synthesize + glucotoricoids, cortisol 

7. Melanocyte stimulating hormone: 

Target: melanocytes 

Effect: increases secretion of melanin 

Chapter 18- continued

Hormones of the posterior pituitary (neurohypophiysis) 

(does not synthesize-storage only) 

1. Oxytocin (OT): Target (women): breasts and uterus 

Actions: stimulates milk ejection for lactating mother, stimulates uterine contractions (smooth muscle) during labor. 

2. Antidiuretic hormone (ADH) target: kidney tubules and collecting ducts 

Action: increases H2O reabsorption—-> decreases urine output

(also targets vessel walls to increase blood pressure)

Thyroid Gland: secretes t3, t4 (thyroid hormone) in response to TSH from anterior pituitary 

Targets: almost every cell in body

Actions: increases basal metabolic rate, atp synthesis, increases body temperature, protein synthesis, lower blood cholestrol. 

Both T3, T4 enter blood stream. Both then enter target cell. T4 is converted to T3 in target cell. 

• Golgi produces thryoglobin which donates tyrosine (a.a) in colloid lumen.

“Myxedema”: Hypothyroidism. Symptoms: low bmr, cold, tired. “Goiter” from lack of iodine in diet. (colloid accumlates with or without producing hormone). 

-”Grave’s disease”: Hypothyroidism. Symptoms: high bmr, fast heart rate, sweating, nervousness, weight loss, protruding eyeballs.

*Calcitonin: hormone also produced by thyroid. Can lower blood pressure Ca++ levels by inhbiting osteclasts activity. 

Parathyroid gland: embedded in thyroid. Usually 4 glands. Secretes parthryoid hormone (PTH) 

targets : bones (osteoclasts), kidneys, Ileum, (sm. intestine)

Actions: 1. High osteoclast activity 2. Low calcium excretion 3. Low ca++ absorption

Overall** high blood ca++ levels

Adrenal Glands: On top of each kidney. 2 parts: Cortex and medulla

Cortex: 3 zones- respond to ACTH from anterior pituitary.

1. Glomeruloisa- secretes mineralocorticoids 

2. Fasicuclata- secrets glucocotiocoids (cortisol)

3. Reticularis- secrets androgens 

Medulla - Center of adrenals epinephrine (Some norephrine)

Targets: many body cells

Actions: stress response (fight or flight). 

Pancreas:Alpha cells secrete glucagon (hormone), beta cells secrete insulin (hormone).

(Low blood glucose triggers release)

Stimulates liver  (target) to break down Glycogen and release glucose to blood.

Action: high blood glucose

Pancreas(continued)

Insulin: release is triggered by high blood glucose levels.

Targets: most body cells

Action: assists transport of glucose across cell membrane (into cell) to use for energy (ATP production)

Result**: low blood glucose levels 

Ovaries and testes: 

Ovaries: secrete estrogens and progesterone

Targets: estrogen—> ovaries and other body cells 

Actions: ovaries assist helps follicular development and body regulates sex characteristics 

Target: progesterone—-> uterus 

Actions: prepares uterus for zygote implantation

Testes: secrete androgens (testosterone)

Targets: testes and other body cells 

actions : regulates sperm cell production, body cells regulates sex characteristics

Pineal gland: secretes melatonin 

Target: hypothalamus 

Action: regulates diurnal cycles

Thymus gland: deep to sternum- secretes 

Targets: young T-lymphocytes in thymus

Action- provides immunocompetence to t-cells.