Physiology Unit 2

Endocrine organs are anything that secretes a hormone.

• Primary endocrine organs are organs that their primary purpose is to secrete hormones
• Secondary endocrine organs are organs that does something else as its primary function, but also does secrete hormones.

• Hypothalamus
• pituitary gland
• pineal gland
• thytoid gland
• parathyroid gland
• thumus
• adrenal gland
• pancreas
• gonads

• Heart
• liver
• stomach
• skin
• small intestine
• kidney

• They function together to regulate virtally every body system
• Most hypothalamic hormones act on the pituitary
• Pituitary gland containes two functionally and structurally different sections
• - Anterior (adenohypophysis)
• - Posterior (neurohypophysis)

Adenohypophysis

neurohypophysis

• Hormones are secreted from neurosecretory cells in hypothalamus into blood
• These hormones are then transported through the H-P portal system to the ant. pituitary
• They stimulate the anterior pituitary to secrete hormones

• - Oxytocin and ADH (aka vasopressin) are synthesized in the hypothalamus , packaged, and transported to neural endings in the post pit.
• - Hormones are released from the post pit by exocytosis upon signal from another neuron

• Controlled by neg feedback system
• The short loop feeds from the ant pituitary to the hypothalamus to prevent buildup of excess ant pituitary tropic hormone
• The long loop feeds from the endocrine gland stimulated by the ant pit to the hypoth to inhibit secretion of tropic hormone.
• Essentially they both limit their own secretion
• Axis: Hypothalamus; tropic hormone 1 secretion --- anterior pit; tropic hormone 2 secretion--- endocrine gland; hormone 3 secretion--- target cell response

neurohormones

• ADH (vasopressin) and oxytocin
• They are synthesized in neurons originating in different regions of the hypothalamus
• ADH is synth in the paraventricular nucleus
• Oxcytocin is synth in the suraoptic nucleus
• Following synthesis, these hormones are packaged into secretory vesicles and tranported to the neural endings in the post pit
• The hormone is released by exocytosis when these neurons receive a signal, usually from other neruons

• By the hypothalamic-pituitary portal system which is a series of 2 capillary beds
• After the hypoth secretes tropic hormones into the capillary bed located there, these tropic hormones travel down the infundibulum to the pituitary gland via a protal vein, from which they enter a second capillary bed. The hypothalamic tropic hormones then stimulate or inhibit the release of hormones from the ant pituitary

The hypothalamus releases a tropic hormone that effects the release of another tropic hormone from the ant pituitary; this tropic hormone effects the release of a third hormone from another endocrine gland and this third hormone exerts effects on target cells throughout the body.

• tropic hormones
• regulate the secretion of other hormones

• Prolactin releasing hormone (PRH)---- stimulates prolactin--- stimulates mammary glands
• Prolactin inhibiting hormone (PIH) aka dopamine---- inhibits prolactin

Thyrotropin releasing hormone (TRH)---- stimulates the release of TSH--- TSH then stimulates secretion of thyroid hormones by the thyroid

• Corticotropin releasing hormone (CRH)--- stimulates the release of adrenocorticotropic hormone (ACTH)---ACTH then stim secretion of other hormones by the adrenal cortex
• Growth hormone releasing hormone (GHRH)--- stimulates secretion of GH --- GH regulates growth and energy metabolism but also fuction as a tropic hormone by stimulating the secretion of insulin-like growth factors (IGFs) by the liver

Growth hormone inhibiting hormone (GHIH) aka somatostatin--- inhibits release of GH

Gonadotropin releasing hormone (GnRH)---- stim both FSH and LH--- LH stimulates ovulation and secretion of sex hormones; FSH promotes development of reproductive cells (eggs and sperm) and stim secretion of estrogens and inhibin

• PRH
• PIH (dopamine)
• TRH
• CRH
• GHRH
• GHIH (somatostatin)
• GnRH

• Prolactin releasing hormone stimulates prolactin
• (mammary glands- breasts)

• Prolactin inhibiting hormone inhibits prolactin
• (mammary glands- breasts)

• Thyrotropin releasing hormone stim TSH
• (thyroid- releases thyroid hormones)

• Corticotropin releasing hormone stimulates adrenocorticotropic hormone ACTH
• (adrenal cortex- releases cortisol)

• Growth hormone releasing hormone stimulates GH
• (Liver and other cells throughout the body- releases insulin like growth factors IGF)

• Growth hormone inhibiting hormone inhibits GH
• (liver and other cells throughout the body)

• Gonadotropin releasing hormone stim LH and FSH
• (gonads- FSH promotes development of sex cells and stimulates the secretion of inhibin in both males and females; LH stimulates secretion of androgens in males and secretes estrogens and progesterone in females)

• Rate of hormone secretion
• - **Inhibition negative feedback
• - Circadian rhythms- mechanism not well understood, but rhythm depends on neural and endocrine input
• Carrier protien binding
• - Lipophilic hormones are transported this way which increases the half-life of the hormones
• -**Only the concentrations of unbound hormones affects the binding of hormone receptor. (active pool)
• Clearance rate
• - aka hormone metabolism
• - most hormones are metabolized by the target cell itself
• - hormones are degraded by enzymes located in lysosomes

two hormones have oppposite effects

• two hormones have the same effect and the net effect equals the sum of the individual effects
• - epinepherine and norepinepherine

two hormones that have the same effect and the net effect is greater than the sum of the individual effects

• one hormone is neeeded for another hormone to exert its actions
• - parathyroid secretes parathyroid hormone and activates calcitriol