Homeostasis and the Endocrine System

Question 1

Define the term homeostasis

Answer 1

Homeostasis is the property that maintains and regulates the internal environment by adjusting biochemical pathways and physiological processes.

Question 2

What are the steps in homeostasis?

Answer 2

stimulus, receptor, control center, effector

Question 3

What are examples of local regulation?

Answer 3

autonomic reflexes, chemical factors

Question 4

What are examples of central regulation?

Answer 4

nervous system via autonomic processes, endocrine system via signals through hormones

Question 5

What is negative feedback and provide an example relating to body temperature control.

Answer 5

negative feedback counteracts imbalances. if body temp falls, blood vessels constrict to conserve heat, shivering generates heat and heat is retained. if body temp rises, blood vessels dilate to promote heat loss, sweat gland secrete fluid and as it evaporates heat is lost.

Question 6

Give an example of negative feedback with body water control.

Answer 6

if dehydration occurs, vasopressin helps increase water retention, aldosterone helps increase Na+ retention and reabsorption.

Question 7

Give an example of negative feedback with blood glucose regulation.

Answer 7

high blood sugar signals the release of insulin from the pancreas, which stimulates glycogen formation and glucose uptake from the blood which lowers blood sugar. low blood sugar signals the release of glucagon from the pancreas to stimulate glycogen breakdown into glucose which raises blood sugar.

Question 8

What is positive feedback and provide an example relating to the initiation of labour.

Answer 8

positive feedback reinforces and amplifies an initiating stimulus. In labour, the baby’s head pushes against the cervix, which triggers nerve impulses from the cervix transmitted to the brain. this stimulates the pituitary gland to secrete oxytocin which is carried in the bloodstream to the uterus, which stimulates uterine contractions and pushes the baby towards the cervix.

Question 9

Give an example of positive feedback in blood clotting.

Answer 9

an injured blood vessels cause platelets to aggregate at the injured site, which releases chemicals that attract more platelets. this loop repeats until a platelet plug is formed.

Question 10

What is physiological acclimatisation

Answer 10

it is adjustments to a change in the environment to allow optimal function. it sets a new baseline for homeostasis. it can occur for a short period of time. it is an adaption usually to the natural environment. it can be reversed or permanent.

Question 11

What is the function of the endocrine system?

Answer 11

the endocrine system is responsible for hormone secretion, growth and development, and thermal regulation.

Question 12

What are hormones and the three types of hormone pathways?

Answer 12

hormones are messengers that circulate through different pathways. these pathways are:
humoral - blood (eg capillary blood contains low conc of Ca2+ which stimulates secretion of PTH to increase Ca2+)
neural - nerves and spinal cord (eg. preganglionic sympathetic fibres stimulate adrenal medulla cells to secrete catecholamines)
hormonal - hormone release (eg. the hypothalamus secretes hormones that stimulate other endocrine glands to secrete hormones)

Question 13

Name and describe the two types of hormone interactions with target cells.

Answer 13

water soluble - interacts with membrane receptors to initiate signal transduction, circulates freely in blood to target tissues (eg insulin, GH, prolactin)

lipid soluble - diffuses across membrane and initiates signal transduction inside the cell, must be bound to a plasma membrane protein in blood circulation, receptors are located inside the cell

Question 14

Give an example of hormones and homeostasis regarding the human growth hormone (HGH).

Answer 14

hypothalamus releases growth hormone releasing hormone (GHRH) or somatostatin (SST), which travels to the anterior pituitary gland. GHRH stimulates the release of GH, while SST signals the inhibition of GH. GH travels to target organs such as the liver or adipose tissues, which cause signalling providing neg/pos feedback to hypothalamus and APG to help maintain balance (neg: insulin growth like factor 1, fatty acids. pos: stomach gastric peptide grehlin)

Question 15

What are antagonistic hormones and give two examples.

Answer 15

set of hormones that have opposite effects on each other. calcitonin and parathyroid hormones which maintain blood Ca2+ levels. insulin and glucagon which maintain blood sugar levels.

Question 16

Explain the afferent and efferent branches of the somatic and autonomic nervous system.

Answer 16

afferent, sensory, nerve signalling to CNS from voluntary (skin, joints, sense organs, skeletal muscle) and involuntary (visceral receptors) pathways. efferent, motor, neurons travelling from CNS to PNS in the SMS voluntary (skeletal muscle) and the ANS involuntary (glands, heart, smooth muscle)

Question 17

Describe the functions of the autonomic nervous system, and the relative divisions.

Answer 17

ANS maintains homeostasis and alters physiology within the internal environment of the body. divided into parasmpathetic and sympathetic/rest and stress. parasympathetic involves the vagus nerve and has general calming effects, and increases relaxation and digestion. sympathetic is a generally6 excitable system which increases alertness, bp, energy, heart rate and breathing rate.

Question 18

Name and describe the function of the autonomic control centres in the ANS.

Answer 18

hypothalamus is responsible for water balance, temp, and hunger and thirst. the pons is responsible for respiration. the medulla is responsible for respiration, cardiac output, gastric function, vomiting and swallowing.

Question 19

What are sensory receptors and name all the types.

Answer 19

they provide afferent feedback within the PNS. includes mechanoreceptors. photoreceptors, chemoreceptors, thermoreceptors, and nociceptors.

Question 20

Define adrenergic and cholinergic neurons.

Answer 20

adrenergic neurons produce norepinephrine as its neurotransmitter. cholinergic neurons release acetylcholine.

Question 21

Describe the functional differences of the sympathetic and parasympathetic systems.

Answer 21

the sympathetic fibres originates in the thoracolumbar region. the neurotransmitters are acetylcholine and norepinephrine (sweat, adrenal medulla respectively). contain adrenergic receptors that signal via G protein complexes.

the parasympathetic fibres originates in the craniosacral region. the neurotransmitter is acetylcholine. contain cholinergic receptors via either G protein coupled or gated ion channels.

Question 22

Describe the three neurotransmitter and fibre type arrangements.

Answer 22

acetylcholine is a cholinergic fibre responsible for all pre-ganglionic fibres of both divisions, al post ganglionic nerve fibres of parasympathetic, and post ganglionic fibres of sympathetic for sweating

norepinephrine is an adrenergic fibre responsible for most post ganglionic fibres of sympathetic, sometimes released from adrenal medulla.

epinephrine is not a fibre, mainly acts as a hormone. always released from cells in the adrenal medulla

Question 23

Describe how G protein receptors work.

Answer 23

a signal molecule joins to a receptor to activate it. a protein becomes activated as GTP binds to release GDP, which causes the protein to activate the effector enzyme.

Gs and Gi regulate the activity of adenylyl cyclase and resulting formation of cAMP. Gq is coupled to phospolipase CD and signals via inositol triphosphate and release of intracellular calcium.