slide set 3.2 - chapter 6 and 7 (homeostasis)

usually part negative feedback loop

• Simplest mechanism
• when an endocrine gland is sensitive to the physiological changes produced by its target cells
• ex. PTH = ↑ plasma calcium

• endocrine secretion may also be regulated by a hormone produced by another gland
• ex. estrogen form ovary feeds back to Pit to regulate FSH

• 1. plasma concentration of thyroid hormones ↓ (ex. T4 AND T3)
• 2. the anterior pituitary secretes TSH
• 3. thyroid in turn secretes TH
• 4. TH inhibits further secretion of TSH

• PTH controls blood calcium concentration (Ca++)
• acts to ↑ while calcitonin works to ↓

• due to lactation, blood Ca concentration is ↓
• the change is sensed by the parathyroid
• PTH stimulates osteoclasts in bone to release more Ca++ from storage in bone tissue
• this ↑ maternal blood Ca++ concentration to set point

• 1. integrates functions that maintain chemical and temperature homeostasis
• function with the limbic system
• 2. controls the release of hormones form the anterior and posterior pituitary

• to regulate temperature, integration of autonomic endocrine and skeblemotor must occur
• the set point for the body is normal temperature
• the hypothalamus contains "feedback detectors" that come from 2 sources:
• 1. peripheral receptors: transmit information through temperature pathways to the CNS
• 2. central receptors : located in the anterior hypothalamus

the anterior hypothalamus = mediates decreases ↓ in heat

lesions = cause hyperthermia

• Electrical stimulations cause:
• dilatation of blood vessels in the skin
• panting
• suppression of shivering

the posterior hypothalamus = mediates heat conversion

lesions = cause hypothermia is an animal is placed in a cold environment

• Microstimulation causes:
• shivering
• constriction of blood vessels in skin

• the hypothalamus is sensitive ti adiposity signals supplied by hormones leptin (secreted by fat cells) and insulin (secreted by pancreas)
• leptin plays a role  in establishing a biological set point for body weight  by modifying the strength in synapses onto neurons

• adiposity signals = modulate anabolic and catabolic pathways in the central nervous system (CNS)
• these pathways control food intake and energy expenditure by influencing behaviour, autonomic activity and metabolic rate
• satiety signals = terminate feeding
• energy balance and fat = control the amounts of leptin and insulin circulating in the blood (adiposity signals)

• 2 adiposity signals, insulin and leptin, are produced in the periphery and travel through the blood to influence neurons in the arcuate nucleus
• some arcuate neurons synthesize and release peptide y (NPY) and agouti-related protein (AgRP) and are inhibited by adiposity signals
• other arcuate neutrons make and release alpha-melanocyte-stimulating hormone (alpha-MSH) and cocaine-amphetamine-related-transcript (CART) and are stimulated by adiposity signals
• NPY/AgRP neurons inhibit the paraventricular nucleus (PVN) and stimulate the lateral hypothalamic area (LHA)
• alpha-MSH/CART neurons do the opposite
• the PVN has a net catabolic action, releasing the neuropeptides CRH and oxytocin and thereby ↓ food intake and ↑ energy expenditure
• the LHA has a net anabolic action, releasing 2 additional neuropeptides, orexin A and melanin-concentrating hormone (MCH), both which will stimulate food intake ↑ and ↓ energy expenditure

 

• 7 hormones are made in the hypothalamus
• 1. TRH
• 2. CRH
• 3. GnRH
• 4. GHRH
• 5. GHIH
• 6. PRF
• 7. PIH

• small but potent
• located in a well protected location in the brain
• located on the ventrical surface of the brain within the skull

• Infundibulum
• stemlike stalk that connects pituitary to the hypothalamus

• the pituitary gland is made of 2 separate glands = anterior gland and posterior
• gland

portal systems = 2 capillary networks in serial arrangements

portal veins = blood vessels that link 2 capillary networks

adenohypophysis (anterior pituitary)

• Divided in 2 parts:
• 1. pars anterior = forms the major portion of the adenohypophysis
• 2. pars intermedia

tissue is composed of irregular clumps of secretory cells supported by fine connective tissue fibres and surrounded by a rich vascular network

• 5 secretory cells exits in the anterior pituitary:
• 1. Somatotrophs*
• secrete GH (growth hormones)
• 2. Corticotrophs
• secretes ACTH (adrenocorticotropic hormone)
• 3. Thyrotrophs
• secrete TSH
• 4. Lactotrophs*
• secrete prolactin (PRL)
• 5. Gonadotrophs
• secrete LH and FSH

Growth hormone (GH) , which are produceed by Somatotrophs, promotes growth by stimulating the liver to produce growth factors that accelerate amino acid transport into the cells

• GH promotes growth of bone, muscle, and other tissues by accelerating amino acid transport into the cells
• all process involve protein metabolism
• GH also stimulates lipid metabolism
• accelerates the mobilization of lipids from cells speeds up lipid catabolism
• this shifts a cells use of nutrients from glucose catabolism → lipid catabolism

• Prolactin (PRL)
• produced by lactotrophs (acidophils) in the anterior pituitary

• Pregnancy
• during pregnancy, PRL promotes development of breasts, anticipating milk secretions

• After birth
• PRL stimulates the mothers mammary glands to produce milk

• Tropic hormones
• have a stimulating effect on other endocrine glands
• stimulates syntesis and secretion of the target hormone

4 trophic hormones are produced and secreted by the basophils of the pars anterior

• 1. TSH
• promotes and maintains growth and development of the thyroid
• causes the thyroid to secrete hormones T3 and T4
• the thyroid regulates metabolism

• 2. ACTH
• promotes and maintains normal growth and development of cortex of the adrenal gland
• also stimulates adrenal cortex to secrete some of its hormones cortisol and aldosterone (act on kidneys)

• 3. FSH
• in females = acts on ovaries 
• stimulates follicle cells to grow towards maturity 
• stimulates follicle cells to secrete estrogen
• in males = development of testes and maintains spermatogenesis
• acts on Sertoli cells

• 4. LH
• in females = stimulates formation and activity of  ovaries
• corpus lutenum = secretes progesterone and estrogen when stimulated by LH
• LH also supports FSH in stimulating maturation of follicle 
• in males = LH secretes interstitial cells in testes to develop and secrete testosterone

• FSH and LH = gonadotropins
• because they stimulate growth and maintenance of gonads

• releasing hormones = influence the secretion of hormones by acidophils and basophils
• negative feedback= this is how the hypothalamus adjusts secretions of the anterior pituitary → adjust secretions of target glands → adjusts activity of their
• target tissues

they rise ↑

• hypothalamus secretes releasing hormones into the blood
• then are carried directly to the hypophyseal portal system

the hypophyseal portal system = carries blood from the hypothalamus directly to adenohypophysis where target cells of releasing hormones are located

• hypothalamus stimulation - from CNS
• pituitary stimulation - from hypothalamic trophic Hs
• endocrine gland stimulation - from pituitary trophic Hs

• ex.:
• GH
• somatomedins
• thyroxin

• all have receptors on many tissues
• stimulate pathways for growth

• neurosecretory cells have their bodies directly in the hypothalamus and their axon terminals in the posterior pituitary

• neuroendocrine system adjusts nutrient supply
• calcitonin, a parathyroid hormone, and vitamin D balance calcium ion use
• nervous system and endocrine system regulate reproduction