A&p Ii - Endocrine

Front 1

Comparison of Nervous vs. Endocrine systems

Back 1

Nervous System
• Action potentials and release of neurotransmitter into specific synapses
• Rapid responses (milliseconds)
• Short lived responses

Endocrine System
• Synthesis and release of hormones into interstitial spaces
• Hormones have to diffuse into blood capillaries, travel throughout the entire body
• Slower responses (seconds, minutes,
• Long lasting effects (hours, days)

Both have signaling molecules, but nervous system signaling molecules are sent to a very specific area/synapse; hormones (by definition) must travel throughout the entire body

Front 2

Types of Signaling Molecules

Back 2

Neurotransmitters – affect specific synapses
-Hormones – travels through the whole body
-Paracrine chemicals (=cytokines) - “Local hormones” – not hormones, don’t travel throughout the whole body; released into tissue spaces, only affect a local area – example, happens when you get bit by a mosquito…local swelling, etc.

Front 3

Embryonic development of endocrine glands

Back 3

Invagination (“in-pocketing”) of epithelial tissues – almost all glands start out this way
• Exocrine gland - glands with ducts to the outside (free surface)
• Endocrine glands – “duct-less”, still secreting, but secretions are released into surrounding tissue and diffuse into blood capillaries….duct-less glands

Front 4

Target organ / target tissue / target cells

Back 4

– although hormones travels the whole body, they usually have a specific organ, tissue or cell that it is meant to affect
• Cell, tissue or organ will have receptors that the hormone will bind to or dock at

Front 5

Control of endocrine secretions

Back 5

- almost always involves a negative feedback
-Change in an internal or external condition activates mechanism to produce change in the opposite direction
-example, Serum Calcium levels – acceptable upper level, go above – hypercalcemia (excess Ca++); acceptable lower level, go below – hypocalcemia (deficient Ca++)
- Calcium levels decrease, PTH levels rise b/c of production by the parathyroid gland, calcium begins to increase, calcitonin rises, calcium decreases…

Front 6

3 main chemical categories of hormones

Back 6

Steriods
- Lipid hormones, synthesized from cholesterol
- Adrenal cortex, sex hormones,
- How do steroids work
o Easily enter into cells(by diffusion)
o Bind with intracellular receptors (usually in the nucleoplasm)
o Activate specific genes (mRNA →protein synthesis – target cell is making a protein that it wasn’t making before)
-Proteins / peptides
- Chains of amino acids
- Pituitary, parathyroids,
-Amines
- Smaller then proteins or peptides, made from amino acids
- Adrenal medulla – epinephrine and norepiephrine

Front 7

Cellular mechanisms for hormone effects

Back 7

Steroids affect their target cells one way, Proteins and Amines hormones work in a totally different fashion

Steroids:
- since they are lipids, steroids easily cross cell membranes, entering inside cells.
- steroids bind to intracellular receptors that are either in the cytoplasm or nucleoplasm.
- the steroid-receptor complex will activate particular genes in the target cells, causing synthesis of mRNA and resulting in the production of a protein(s) that was not present before the hormone entered the cell.

Proteins and Amines
- Can’t enter cells b/c of polarity and/or size (too big)
- Must bind w/cell surface receptors
- Binding activates a second-messenger mechanism (Biochemical cascades - domino effect…..this happens, which causes that to happen…, etc.)

Front 8

A typical Second-messenger mechanism…….(there are others besides this one)

Back 8

• Target cells for a protein or amine hormone (1st messenger) must have receptors on the surface
• Hormone binds with cell-surface receptor causing:
• Adenylate cyclase to be activated and released into the target cell cytoplasm;
• this causes ATP to become Cyclic AMP (cAMP)
• cAMP activates inactive Protein Kinases (PKs)
• PKs activate Phosphorylase enzymes
• The active phosphorylase enzymes will phosphorylate (add a phosphate to …) specific proteins in the target cell (phosphorylation tends to energize molecules)
• Biochemical pathway now speeds up

Front 9

Pituitary Gland (=hypophysis)

Back 9

actually 2 distinctly different glands wrapped up together

- Neurohypophysis – smaller, posterior lobe Adenohypophysis – larger, anterior lobe

Front 10

Neurohypophysis

Back 10

smaller, posterior lobe of pituitary gland
o Neurosecretory cells – former, modified neurons; cell bodies are in the hypothalamus, and synthesize the hormones; “axons” travel through the infundibulum, delivering the hormones to the neurohypophysis for storage and release
-
o Stores and releases 2 hormones that are synthesized (made) in the hypothalamus
 ADH, anti-diuretic hormone (=vasopressin)
• Primary target: kidneys
• Effect: increase water retention
• Secondary target: small arteries
• RARE Effect: vasoconstriction (requires very high ADH- most often happens during hemorrhage, significant blood loss, cardiovascular shock)
• Alcohol suppresses the release of ADH
 Oxytocin (synthetic version is called pitocin )
• Primary effect: uterine contractions
• Secondary effect: stimulates “letting down” of milk into the nipples
• Release by both sexes during orgasm
• Mood –enhancing and bonding effect

Front 11

Adenohypophysis

Back 11

larger, anterior lobe of pituitary gland
o No nerve fiber connections b/t here and the hypothalamus
o Circulatory system (cardiovascular) connection – extensive network of capillaries
 Capillaries are the exchange vessels, where substances can get into or out of the blood
 Primary Capillary plexus – in hypothalamus → blood from primary plexus drains into hypophyseal portal vein (in infundibulum) → drains into another network of capillaries in the adenohypophysis (secondary capillary plexus)

o Hypothalamus controls the adenohypophysis by producing a series of:
 Releasing hormones (RHs) and inhibiting hormones (IHs)
• Made (synthesized) in the hypothalamus
• Target: adenohypophysis
 Hypothalamus → adenohypophysis → thyroid gland → (produces) T3 and T4 increase general metabolic rates
• Hypothalamus detects stimuli - low levels of T3, T4; cold environment (esp. in infants); high altitudes; stress – produces TSH – RH (thyroid stim hormone, releasing hormone)
• Adenohypophysis – target cells in the adenohypophysis which the TSH-RH will dock / bind at – adenohypophysis now makes TSH (complete different from TSH-RH) diffuses into secondary capillary plexus; goes to thyroid gland
• Thyroid gland stimulated by TSH which then produces T3 and T4

Front 12

6 main Hormones from the adenohypophosis

Back 12

o TSH, thyroid-stimulating hormone = thyrotropin, thyrotropic hormone
 Tropin = cause the production of other homones
 Stimulates release of thyroid metabolic hormones (T3, T4)
o ACTH, adrenocorticotropic hormone = corticotropin
 Made when under stress
 Stimulates adrenal cortex
 Makes a number of different hormones
 Causes large increase in a class of hormones called glucocorticoids (coritsol, etc)
 Cause moderate / mild increase in mineralocorticoids (aldosterone, etc.)
o Prolactin
 Stimulates milk production
 Also responsible for breast tenderness prior to menstrual period (estrogen and progesterone are bottomed out during period, but high just before)
 Both P-RH (made when estrogen and progesterone are high) and P-IH (made when estrogen and progesterone are low)
 No effect on males
o GH, growth hormone = somatotropin
 Stimulates growth in any tissue capable of growing; especially targets the bones (long bones)
 3 periods of life when huge growth spurts
• Prior to birth
• Birth to 18 months
• Puberty
 Increase uptake of amino acids into cells
 Increase blood sugar via liver glycogenolysis
 Increase mobilization and catabolism of fats
 Increase rates of protein synthesis
 Some of the things that the growth hormone does is done directly to the cells of the body
 Many of the things that growth hormone does is done indirectly
• Stimulates production of a group of hormones called either somatomedins or/aka IGFs (insulin-like growth factors)
o Gonadotropins
 FSH, follicle-stimulating hormone
• Females – stimulates development of “egg”-containing ovarian follicles, and maturation of the “egg” (oocyte)
• Males – stimulates spermatogenesis in the testes
•
 LH, luteinizing hormone (in women;) called ICSH, Interstitial Cell-stimulating hormone in men
• Women – stimulates ovulation, and causes development of the corpus luteum (yellow body) which secretes estrogen and progesterone.
• Men – interstitial cells of Leydig (b/t tubes in the testes) – produce androgens (testosterone, etc.);
• men have constant levels of this hormone, whereas women cycle levels of this hormone