Homeostasis and endocrine

Homeostasis meaning

regulation of internal conditions of a cell/organism to maintain optimum conditions for function in response to internal & external changes

How does this change occur (homeostasis)

• requires a stimulus – something to respond to

• picked up by a receptor

• then sends signals to the coordination centre perform some action to respond to that until it bak to optimum

• an effector produces response

receptor

detects stimuli (change in environment)

effector

muscles/glands that brings changes which restores optimum levels

coordination centre

receives and processes information from the receptors (eg brain, spinal cord, pancreas)

pathway of control system for body temperature

1. stimulus→ change in temperature

2. receptor → skin

3. coordination centre→ brain/hypothalamus

4. effector → skin/muscles

Pathway of control system for water content of body

1. stimulus- change of water content in blood

2. receptor - brain

3. coordination centre- pituitary gland

4. effector - kidneys

pathway control system for blood glucose

1. stimulus - change in blood glucose

2. receptor - pancreas

3. coordination centre - pancreas

4. effector - liver

How does the body control water content

1. if too much water in blood

2. hypothalamus detects too much water in blood

3. pituitary gland releases less ADH

4. kidney absorbs more blood

5. so more water reaches bladder (dilutes urine)

6. blood level returns to normal

What controls centre coordinates body temperature

thermoregulatory centre in the hypothalamus of the brain

How does your body detect temp change?

• the centre contains receptors that are sensitive to temp changes in the blood flowing through the brain

• temp receptors in he skin send extra info to the thermoregulatory centre via sensory neurons

• the receptors are so sensitive the can detect a 0.5 degree celsius change

cooling down

when core body temp begins to rise impulses sent via thermoregulatory centre to body so more energy is transferred to surroundings to cool you down

sweating

• blood close to surface of skin heating it up

• liquid sweat turns into gas (evaporates)

• it takes heat from skin

• skin loses heat it cools down

vasodilation

• blood carries most of the heat energy around body

• capillaries underneath skin that can be filled with blood if you get too hot

• brings blood closer to surface of skin so more heat can be lost

warming up

• if you get to cold the rate of enzyme controlled reactions fall too low

• not enough respiration → danger of death

• impulses sent to thermoregulatory system centre to prevent cooling down be preventing energy transfer to environment

vasoconstriction

• capillaries under your skin get (shut off)

• takes blood away from surface of skin so less heat can be lost

piloerection (goosebumps)

• the hairs trap layer of air next to skin which is then left warmed by the body heat 

• the air becomes an insulating layer

shivering

• muscles require energy ( from respiration) to contract

• during respiration some energy is always lost as heat

Endocrine system

• made up of glands that secrete hormones into the bloodstream

• the effects are slower than nervous system but have a longer lasting effect 

pituitary gland

• releases hormone ADH

• controls growth and stimulates other glands like thyroid, ovaries and testes

thyroid gland

• releases hormone thyroxine

• controls metabolic rate

adrenal gland

• hormone- adrenaline

• triggers fight or flight → prepares body for stressful situations

pancreas

• releases hormones insulin and glucagon

• controls blood glucose levels

ovary

• releases hormone oestrogen

• controls development of sexual characteristics & menstrual cycle

testes

• releases hormone testosterone

• controls development of sexualcharacteristics and sperm

hormones

• chemical messages produced by gland

• have an effect in target organ and travel in the blood stream

glucose

sugar

glucagon

hormone

glycogen

glucose stored (as larger molecules) in the liver/muscles

how the pancreas controls blood glucose levels

• insulin moves glucose in blood into cells to be used

• soluble glucose can also be turned into the insoluble carbohydrate glycogen

• glucagon is a hormone that stimulates the liver to turn glycogen back into glucose

high glucose levels in blood

• pancreas produces insulin to lower glucose levels in blood

• glucose diffuses into liver 

• (glucose is used in respiration)

• forms chains of glucose → glycogen

• glycogen stored in liver

low glucose levels

• pancreas releases glucagon

• breaks up glycogen in liver

• now glucose

• diffuses back into blood stream

diabetes

occurs when glucose control goes wrong

type 1

• pancreas doesn’t produce insulin

• glucose levels are uncontrollably high

• treated with insulin injections

type 2

• insulin is produced but liver cells no longer responds to it

• people who are obese are at risk

• controlled by limiting carbs/sugar in diet and exercise

the kidney

the main job of the kidneys is to control the water balance of the body

what do kidneys do

• if little water kidneys conserve it → produce very little, very concentrated urine

• control concentration of mineral ions so if excess mineral ions → lost through sweat/urine

• too much water so aim to excrete it → produces lots of dilute urine

What removes excess water, ions and urea from the body?

The kidneys remove excess water, ions and urea in the urine.

What happens to excess amino acids from the diet?

 They are deaminated in the liver to form ammonia.

Why must ammonia be converted to urea?

Ammonia is toxic.

What do the kidneys produce by filtration and selective reabsorption?

Urine.

What useful substances are selectively reabsorbed?

Sugar and as much water as the body needs.

Which substances are excreted in urine?

 Urea, excess ions and water.

What controls the water level in the body?

by the negative feedback system controlled by the hormone ADH 

When is ADH released?

When the blood is too concentrated.

What does ADH cause the kidney tubules to become?

More permeable.

What does increased tubule permeability allow?

More water to be reabsorbed back into the blood.

Why does protein remain in the blood plasma rather than the filtrate?

the molecules are too large to pass through the filter

How does ADH affect production and concentration of urine by the kidneys? (4)

• high levels of ADH increase water reabsorption

• from kidney tubules

• so) ADH increases the concentration (of urine) 

• (so) ADH decreases the volume (of urine) 

Describe what happens to glucose, protein and urea in kidneys (4)

•  glucose and urea are filtered (out of the blood) 

• protein is not filtered (out of the blood) 

• all glucose reabsorbed 

• urea passes out in urine / not absorbed

kidney stones

• high salt and minerals in your diet can lead to stones precipitating out

• extremely painful

• have to be excreted from the body in the urine

renal damage/failure

• the kidney no longer able to filter the blood effectively

• plasma not properly reabsorbed

• protein and cells pass through bowman’s capsule

kidney failure

• a person can survive with only one kidney

• no working kidney → death

• options : dialysis or transplantation

kidney dialysis

transplantation

• organ removed from either dead person or living person if not an essential organ

• inserted and connected to patient

• damaged organs sometimes removed

• donor organ not always connected into position of old organ

advantages and disadvantages of transplantation

Advantages	Disadvantages
can live relatively normal life	shortage of donors
immunosuppressant drugs are relatively cheap	need tissue match lited transplant life span (10 years) immunosuppressant drugs needed for rest of life

advantages and disadvantages of dialysis

Advantages	Disadvantages
machines available	time consuming
no need for tissue matching	expensive longterm (30K a year) diet must be carefully controlled

kidney disease

• filtration in the kidneys doesn’t work properly so proteins are pushed out into urine as they are too big

• glucose in urine = kidney failure

• protein in urine = kidney failure too big to filter back into blood

• negative feedback

• if a factor in the internal environment increases or decreases, changes take place to reduce it and restore the original level

• stimulus→ sensor → control→ effector → back to stimulus

• whatever the initial change the response causes the opposite

thyroid

• gland in your neck uses iodine from your diet to produce hormone thyroxine

• thyroxine controls basal metabolic rate of the body

what does your basal metabolic rate determine

• how quickly substances are broken down and built up, how much oxygen your tissues use and the development of the brain in a growing child

• plays a huge role in growth and development

Adrenaline

• important hormone for organisms

• boosts the delivery of oxygen and glucose to brain and muscles

• preparing body for fight or flight

how does adrenaline affect body

once adrenaline is released from adrenal glands effects include :

• heart rate and breathing to increase

• stored glycogen in the liver to be converted to glucose for respiration

• pupils of eyes dilate to let more light

• increased mental awareness

• blood diverted away from digestive system to big muscles

examples of negative feedback (thyroxine + adrenaline)

• if thyroxine levels begin to fall its detected by the brain

• then releases TSH to increase levels (negative feedback)

• adrenaline released by adrenal gland when in danger

• once threat is over system returns to their resting levels

reproductive hormones during puberty

cause secondary sex characteristics to develop

ovulation (+ tests)

• day egg is released

• can conceive within 6 days of ovulation

• ovulation test measures the levels of LH in urine

• → ovulation will occur 24-48 hrs after a positive ovulation test

menstrual cycle (hormones)

1. FSH -pituitary gland→ causes follicles to grow and mature then triggers ovary to make oestrogen

2. oestrogen-causes rise in LH, stops production of FSH, starts build up of uterus lining

3. LH → stimulates release of egg

4. progesterone→ inhibits levels of LH and FSH, maintains uterus lining, if egg fertilised prep for baby

empty follicle (yellow body) → releases progesterone

menstrual cycle days

1-7: bleeding uterus lining exits

7-13: FSH causes an egg to start to mature in one of the ovaries

14: LH causes egg to leave & go to oviduct

14-17: egg is able to be fertilised up to a day after

18-28:if not fertilised then oestrogen & progesterone causes lining to begin to break down

hormonal contraception

• contraceptive pill

• implant

• injection

• skin patch

• IUS

Non-hormonal contraception

• tubal ligation

• condom

• diaphram

• IUD

• Vasectomy

contraceptive pill (how it works, risks doses)

• mixed pill → low doses of oestrogen and progesterone

• → inhibits production and release of FSH

• → affects uterus lining preventing implantation, makes mucus thick preventing sperm from getting through

• risks → raised blood pressure, thrombosis, breast cancer

• take a pill every day one week break in a month

mini pill

progestogen only pill → inhibits LH + FSH

if they don’t take pill everyday they’re at risk of pregnancy as egg will mature and be released

implant

• release progesterone

• lasts 3 years

• 99.95% effective

injections

progesterone

lasts 12 weeks

skin patch

oestrogen and progesterone

lasts 7 days

condom

collects semen

prevents STDs

diaphram

thin rubber diaphragm

prevents entry of sperm

intrauterine devices IUD

• small structure inserted into uterus by doctor

• last 3-5 years

• contain copper and prevent any early embryos implanting into lining of uterus

• IUS contains progesterone→ prevents buildup of lining which could create period problems

abstinence

some religious groups don’t accept contraception

no intercourse around ovulation

rhythm method

unreliable

ovulation indicators help

surgical methods

• vasectomy→ sperm duct cut & tied prevent sperm getting out of testes

• tubal ligation→ oviducts cut and tied

• anaesthetic needed

• surgically sterilised