biol121 - week 5

endocrine system

the endocrine system coordinates functioning between different organs through hormones, which are released into the bloodstream from specific types of cells within endocrine (ductless) glands. once in circulation, hormones affect function of target tissue, which may be another endocrine gland of an end organ

endocrine

hormones

• secretion direct to bloodstream

• no ducts

• insulin and glucagon

excocrine

• secretion into epithelial surfaces

• via ducts

• sweat, mucus, digestive enzymes

what does the endocrine system do?

• regulate growth

• controls reproduction (pregnancy and menopause)

• regulates sleep

• allows body to cope with stress, trauma and infection

• regulates circulation and red blood cell production

• controls digestion and absorption of food

hormones

blood borne chemical messenger, specific target, low concentration

• hormones bind to receptors

receptors

specialised proteins in or on cells) are located in: the cell membrane, cytoplasm and nucleus

target cell - when specific receptors are present

• each cell can respond to w wide variety of hormones, wide variety of receptors

• determines hormone sensitivity and functionality of the tissues

water soluble hormones

• interacts with receptors on/in cell membrane

• effects are ‘indirect’ (via second messenger systems)most hormones (insulin, PTH, adrenaline)

fat soluble hormones

• can easily cross the cell membrane

• interacts with receptors inside cell

• effets are ‘direct’

• cortisol, aldosterone, sex hormones, vitamin D, thyroid hormone

mechanisms of action

• rates of enzymatic reaction: change shape and function of the enzyme

• controlling transport: open/close membrane channel

• controlling gene expression: turn on/off, increase/decrease rate of protein production

communication

commands from endocrine and nervous system, communicate and control with other, endocrine uses chemical messengers - hormones and the nervous system uses nerve impluses

hypothalamus

• command centre of endocrine system

• nervous system and endocrine intercept - structurally connected

• highest level of endocrine control in the body

• hypothalamus can produce own hormones - in nerves stored and released to the posterior pituitary

anterior pituitary

• makes and releases OWN hormones

• lots of hormones

• connection via capillary beds

hypothalamus release hormones (releasing or inhibiting), travels down through blood vessel to bind to receptors in AP, stimulates and produces own hormones into the bloodstream

posterior pituitary

• stores and releases hormones made by the hypothalamus

• two hormones

• connections via nerve fibres

specialised nerves sitting in the hypothalamus that released hormones, not direct blood connection, hormones travels down axons on nerves then stored and released in the posterior pituitary

connected to hypothalamus via direct nervous connection or hormonal signals secreted by the anterior pituitary hormones

hormones in posterior pituitary

oxytocin (OT): controls uterine contractions at onset of labour, controls milk release from lactating breast

anti-diuretic (ADH) hormone: acts on kidneys to reabsorb water, regulates blood osmolarity, aka vasopressin

thyroid gland

• sensory inputs from the environment

• releasing RH (releasing = go signal) and inhibiting IH (inhibiting - stop signal) hormones from the hypothalamus control release of anterior pituitary hormones = TSH - thyroid gland

thyroid gland cont

butterfly shaped organ

two hormones

thyroid hormones: TH, (T3, T4/thyroxine) - how many iodine atoms are apart of that structure, converts iodine in thyroid hormones

• need iodine

calcitonin

• decrease blood calcium

thyroid gland functions

• increase basal metabolic rate

• increased metabolic rate means increased heat production

• stimulate protein synthesis and usage of fuels to make ATP

• enhanced sympathetic activity (increased HR and BR)

• essential for normal growth and development (especially skeletal and nervous system)

• negative feedback system

thyroid gland steps

hypothalamus secretes hormone - pituitary gland, which tells anterior pituitary gland to secrete a second hormone and release it into the blood stream

hormone - bloodstream - thyroid gland, when it binds to a receptor = causes the thyroid gland to produce and release the thyroid hormones - affecting metabolism, growth and development

adrenal gland

essential for life

superior to kidney

• paired glands

• to regions: cortex and medulla

hypothalamus controls the adrenal gland function - secretion of regulatory hormones to control activity of the anterior lobes of the pituitary gland & control of sympathetic output to adrenal medulla

is a modified part of the SNS that secretes adrenaline and nor adrenaline

metabolic effects and CVS effects of adrenal medulla

increases amount of energy for immediate use:

glycogenolysis: releases glucose

lipolysis

• increases cardiac output (increase HR and SV)

• vasodilation of coronary and skeletal muscle blood vessels

• bronchodilation

• vasoconstriction of blood vessels to non-essential tissues (GIT, skin, kidneys)

glucose homeostasis

our cells use glucose to produce ATP and our cells use ATP to power important biological functions

• protein synthesis. muscle contraction, nerve impulse transmission

the brain consumes LOTS of glucose derived energy

absorption: glucose is out gut has been absorbed across the gut wall into the bloodstream

pancreas is key

glucose is regulated by - insulin, glucagon and other hormones

HYPERglycemia

after you eat:

• blood glucose INcreases

• INsulin is released: decrease blood sugar levels

• beta cells produce insulin

• usage and storage

HYPOglycemia

HYPOglycemia

when you are fasting

• blood glucose decreases

• glucAgon is released (alpha cells): raises blood sugar levels

• releases stores

• make new glucose

glucose homeostasis steps

• increase in blood glucose levels: b cells of the pancreas release insulin and this causes glucose to be taken into cells to be stored as glucagon or used for energy (cellular respiration) - decrease in blood glucose levels

• decrease in blood glucose levels: cause alpha cells to release glucagon and this increases blood glucose levels by hepatic gluconeogenesis (make new glucose) and glycogenolysis (break down glycogen to glucose)

glucose homeostasis terms

• glucose: a simple sugar

• glucagon: hormone to increase BGL

• glycogen: stored glucose

• gluconeogenesis: make new glucose

• glycogenolysis: break glycogen (to glucose)

calcium homeostasis

calcium is important in many physiological processes

• structural component of bones and teeth (99%)

• maintains normal excitability of nerve and muscle cells

• muscle contraction (skeletal and cardiac)

• co-factor in many important reactions

• milk production

calcium metabolism regulated by

• parathyroid glands are key

1. parathyroid hormone (PTH)

2. vitamind D (calcitriol)

3. calcitonin (minor significance in adult humans and more relevant in growing individuals)

HYPOcalcemia

lower than normal

factors that increase blood calcium level

parathyroid glands release PTH

oestoclasts release calcium from the bone

calcium is reabsorbed from urine by the kidney’s

calcium absorption in the small intestine increases via vitamin D synthesis

HYPERcalcaemia

too high

factors that decrease blood calcium level

thyroid gland releases calcitonin

osteoclast activity is inhibited and increased osteoblast action

calcium reabsorption in the kidneys decreases

calcium level in blood decreases

calcium homeostasis steps

• increase in calcium blood levels - increase calcitonin by thyroid - decrease osteoblast activity, decrease bone clearance, increase calcium secreted from the kidney’s = decrease in calcium blood levels

• decrease in calcium blood levels - increase in PTH (parathyroid hormone) - increase in osteoclasts, increase bone clearance, increase calcium reabsorption from kidneys, increase calcium absorption into GIT

osteoclasts: cut, break down calcium to get calcium for bone clearance

osteoblasts: build calcium

oxytocin: positive feedback loop

contraction of the uterus: changes in homeostatic balance

stretching of the cervix = change monitored by the stretch receptors in the cervix, which sends details of change to the hypothalamus, this integrates signals, processes and sends instructions, the hypothalamus releases the oxytocin

muscle sin the uterus walls contract and the presence of a baby stretch the cervix more = more chemicals and increase stretching of the cervix

• this positive feedback loop amplifies stimulus, until the presence of the stimulus is no longer there

TRH and TSH - negative feedback loop

cold infant with low metabolic rate

THR is released by the hypothalamus and arrives at the anterior pituitary which stimulates the production of TSH at the anterior pituitary, which then activates T4 and T3 at the thyroid this then affects

• metabolic rate, heat production, enhancement of growth, CNS development, enhancement of SNS at muscles, adipose tissue, liver and the heart

• this negative feedback counteracts the stimulus and returns the body to homeostasis