CRS102 - Endocrine

nervous system

-nerve impulses/neurotransmitters
-faster responses, briefer effects, acts on specific target

endocrine system

-slower responses, effects last longer, broader influence
-control system of ductless glands and single cells that secrete chemical messengers

exocrine glands

-secrete products into ducts to surfaces
-sweat glands, sebaceous glands, mucous glands

endocrine glands

-secretes hormones directly into the bloodstream (ductless)
-pituitary, thyroid, parathyroid, adrenal, pineal glands
hypothalamus

hormones

-long-distance chemical signals that travel in blood or lymph throughout the body
-begin causing their activity with the binding to receptors

autocrines

chemicals that exert their effects on the same cells that excrete them

paracrines

act on neighboring cells

lipid soluble

-chemical class of hormones which makes use of transport proteins
-enter target cells because they easily pass plasma membrane
-steroid, thyroid, nitric oxide (NO)

water-soluble

-first messengers --> can deliver messages only as far as the plasma membrane
-needs second messenger inside the cell
-chemical class of hormones that circulate in "free" form
-cannot easily enter the cell
-amine, peptide/protein, eicosanoid

negative feedback mechanism

-maintain homeostasis
-control the secretion of most hormones

regulation of hormones secretion

by one or more of these three mechanisms:
-changes in the extracellular concentration of a non-hormone substance
-stimulation by the nervous system
-stimulation by a hormone from another endocrine tissue

hypothalamus

major link between nervous and endocrine system

pituitary

-attached to the hypothalamus by infundibulum
-anterior and posterior pitu

anterior pituitary

adenohypo

posterior pituitary

neurohypophysis

human growth hormone (hGH)

-somatostatin
-stimulates the secretion of insulin-like growth factors that promote growth, protein synthesis
-acts directly on other tissue cells to promote fat break-down (lipolysis)
-anterior pituitary gland

thyroid-stimulating hormone (TSH)

-stimulates synthesis and secretion of thyroid hormones by thyroid
-anterior pituitary gland

follicle-stimulating hormone (FSH)

-ovaries initiates developments of oocytes
-testes stimulates testosterone production
-anterior pituitary gland

luteinizing hormone (LH)

-ovaries stimulate ovulation
-testes stimulate testosterone production
-anterior pituitary gland

prolactin (PRL)

-promotes milk secretion by mammary glands
-gynecomastia
-anterior pituitary gland

gynecomastia

-man

adrenocorticotropic hormone

-corticotropin
-stimulates glucocorticoid secretion by adrenal cortex
-anterior pituitary gland

melanocyte-stimulating hormone

unknown role in humans
-anterior pituitary gland

hormones of the posterior pituitary

-does not synthesize hormones
-stores and releases hormones made by the hypothalamus transported along hypothalamohypophyseal tract

oxytocin

-transported by posterior pituitary gland
-affects the uterus and breasts during and after delivery of the baby
-enhances smooth muscle contraction in the wall of the uterus
-stimulates milk ejection from mammary glands

antidiuretic hormone (ADH)

-vasopressin
-transported by the posterior pituitary gland
-decrease urine production -->kidneys return more water to the blood
-decrease water lost through sweating
-increases blood pressure --> constriction of arterioles

thyroid hormones

-consists of two related iodine-containing compounds
-triiodothyronine (T3) and tetraiodothyronine (T4)
-increase rate of glucose, fat, and protein metabolism in many tissues
-increase body temperature

T3

has two tyrosines with three bound iodine atoms (90%)

T4

-thyroxine
-has two tyrosine molecules plus four bound iodine atoms (10%)

osteoclasts

cells that breakdown bones

calcitonin

inhibits osteoclasts thus decreasing blood Ca2+ level

calcitriol

stimulates increased absorption of Ca2+ from foods which increases Ca2+ level

parathyroid hormone (PTH)

-stimulates kidneys to release calcitriol
-dehydration opposes action of this hormone

pancreatic islets

-islets of langerhans
-both exocrine and endocrine gland
-roughly 99% of cells produce digestive enzymes
-Alpha, Beta, Delta, F

Alpha cells

-A cells
-secrete glucagon --> raises blood sugar

Beta Cells

-B cells
-secrete insulin --> lowers blood sugar

insulin

-target tissues --> liver, adipose tissue, muscle, satiety center in the hypothalamus
-increases the uptake of glucose and amino acids by cells
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glucose

-used for energy
-stored as glycogen
-converted into fats

Delta Cells

-D cells
-secrete somatostatin --> inhibits both insulin and glucagon

F cells

-secrete pancreatic peptide --> inhibits somatostatin, gallbladder contraction, secretion of pancreatic digestive enzymes

other endocrine organs

-gonads, ovaries, testes
-pineal gland
-thymus
-GI tract
-kidneys
placenta

gastrointestinal tract

produces gastrin, secretin, and and cholecystokinin

kidneys

produce erythropoietin --> stimulates RBC production

placenta

secretes human chronic gonadotropin --> essential for the maintenance of pregnancy

effects of aging

-gradual decrease in secretion rate of most hormones
-some decreases are secondary to gradual decreases in physical activity