Section 6 - 16 Homeostasis Flashcards
Define - Homeostasis
- Maintainance of a constant internal environment within a living organism.
Give 4 examples of homeostasis within a mammal
- Blood pH - optimum enzyme activity, maintaining shape of antibodies
- Core temp - optimum enzyme activity
- Blood glucose conc. - effective energy transfer and maintaining water potential of the blood
- Water potential of blood - maintain correct cellular water potential and structure.
How can homeostasis be controlled?
- Nervous system
- Endocrine system
- A combination of both
What is a feedback loop?
- Stimulus - change
- Receptor - detected change
- Coordinator - thinking
- Effector - doing
What are the two types of feedback?
- Negative - change in conditions, reversed and returned to set point to maintain optimum conditions
- Positive - change detected is increased further away from the optimum condition does not lead to homeostasis. - only good application in pregnancy as oxytocin hormone released to endorse labour.
What is an endotherm?
- Maintaining body temp at set point
- generate heat energy through respiration
- change cellular and physiological processes
- warm blooded animals
What is an ectotherm?
- Rely on external heat energy
- warm/cool body by changing behaviour in response to changing conditions
- cold blooded
How do ectotherms control temperature?
- basking in sun
- taking shelter
- gaining warmth from ground or rocks
How do endotherms get warmer?
- vasoconstiction
- shivering
- hair raising
- increased metabolic rate
- decreased sweating
- behaviour - finding heat
How do endotherms lose heat?
- vasodilation
- increased sweating
- lowering hair
- behaviour - finding cooler
What are the two types of gland in the endocrine system?
- Exocrine (chemicals outside body)
- Endocrine (chemicals within body)
What are some examples of endocrine glands?
- Pituitary
- Thyroid
- Parathyroid
- Adrenals
- Pancreas
- Ovaries/uterus
- Prostate/testes
What effect do hormones have?
- Effect permeability of cell membrane
- cause release of the second messenger inside a cell
- diffuse into cell and promote/inhibit transcription
Why do blood glucose levels need to be controlled?
- Hypoglycamia (too little) and hyperglycaemia (too much) can kill cells due to the effect on water potential of blood and tissue fluid.
- Required in respiration
- Required for the manufacture of many other cellular products
Explain how blood glucose is detected
- Monitored by pancreas
- In islets of Langerhans (tissue wall of pancreas) - which acts as receptor and cendocrine cell
- Two types of cell:
- Alpha cells - larger, detect low glucose conc. and secrete glucogen
- Beta cells - smaller, detect high glocose conc. and secrete insulin
- Capillaries run throughout so blood is constantly monitored.
What are the two types of cell within the islets of Langerhans?
- Alpha cells - larger, detect low glucose conc. and secrete glucogen
- Beta cells - smaller, detect high glucose conc. and secrete insulin
What are some factors that affect blood glucose conc.?
- Diet
- Glycogen converted into glucose in the liver
- from gluconeogenesis
Where is glycogen stored?
Liver
What three processes occur in the liver?
- Glycogenesis - synthesis of glycogen from glucose
- Glycogenolysis - break down of glycogen into glucose
- Gluconeogenesis - synthesis of glucose from lipids, amino acids or nucleic acids
What is Glycogenesis?
- Synthesis of glycogen from glucose
- In liver
What is Glycogenolysis?
- In liver
- break down of glycogen into glucose
What is Gluconeogenesis?
- in liver
- synthesis of glucose from lipids, amino acids or nucleic acids
What is the process of regulating if blood glucose is too high?
- Beta cells in islets of Langerhans detect change
- Immediately secrete insulin into the bloodstream
- Insulin binds to receptors on the surface of muscle and liver cells
- In Liver cells - activates enzymes that convert glucose to glycogen (Glycogenesis)
- In muscle cells - control uptake of glucose into cells regulating the activity to channel proteins on cell surface membrane
- Excess glucose can also undergo conversion to far.
How is blood glucose regulated if too low?
- Alpha cells in islets of langerhans detect low glucose levels
- Glucagon secreted into the bloodstream
- glucagon binds to receptors on the surface of muscle and liver cells
- Liver cells - enzyme to convert glycogen to glucose (glycogenolysis)
- Both cells - enzymes to convert glycerol and amino acids into glucose (Gluconeogenesis)
What does adrenaline do?
- Increase blood glucose levels
- Attaching to protein receptors on the cell-surface membrane of target cells
- Activate enzyme that causes the breakdown of glycogen to glucose in liver cells
- Causing glycogenolysis for rapid response.
What is the second messenger model?
- Adrenaline (1st messenger) bind to transmembrane protein receptor site
- Bind cause receptor site to change in shape and adenyl cyclase is activated
- Activated adenyl cyclase converts ATP to cAMP
- cAMP binds to protein kinase enzyme (inactive) changing shape and activating it.
- Enzyme converts glycogen to glucose - glycogenolysis
- Glucose uses facilitated diffusion out of the liver cell into the bloodstream
- blood glucose levels increase.
What does insulin do?
- Attach to receptors on surface of target cell
- Controls uptake of glucose by regulating the inclusion of channel proteins in the surface membranes of target cells
- activating enzymes involved in the conversion of glucose to glycogen - glycogenisis.
What does glucagon do?
- Attach to receptors on surface of target cells
- Activating enzymes involved in conversion of glycogen to glucose - glycogenolysis
- Activates enzyme involves in conversion of glycerol and amino acids to glucose - gluconeogensis
What is the role of the liver?
- Found immediately below diaphragm
- Made of cells called hepatocytes
- filters blood from digestive tract
- detoxifies chemical
- regulates blood glucose conc. for the use of hormones
What is diabetes mellitus?
- the inability to metabolise carbohydrates properly especially glucose
- Over 415 million in the world suffer
- 90/5 have type 2
What is type 1 diabetes?
- Insulin dependent
- Unable to produce insulin
- Beginning in childhood with rapid onset of symptoms
- Symptoms - Frequent urination, glucose in the urine, genital itching, weight loss and tiredness
- Usually, caused by autoimmune response attacking beta cells in liver.
How can you control type 1 diabetes?
- Injections 2-4 times a day - can not be tablet as insulin would be digested not used
- Match dose for glucose intake - monitor using biosensors
- Can not be cured - recent trials in transplanting insulin.
What is type 2 diabetes?
- Glycoprotein receptors lost of losing responsiveness
- Also due to the inadequate supply of insulin by the pancreas
- Develops in people over 40
- Develop slowly and symptoms not serve
- People overweight are more likely to develop.
How can type 2 diabetes be controlled?
- Regulate intake of carbohydrates in diet
- Supplement with Injections or drugs that stimulate insulin production
- Can be cured as body can recover through diet changes.
What are the two precesses of the kidney?
- Osmoregulation
- Excretion
What is osmoregulation?
Controls water potential of body fluids by controlling water potential of blood by controlling both the volume and concentration of urine produced.
What is excretion?
- the removal of waste products from metabolism
- eg. urea and creatinine
What are the functional groups of kidney’s?
Nephrons
- 1 million in every kidney
- Start and end in the cortex and extend down into the medulla.
What are the two processes for the production of urine?
- Ultrfiltration - blood filtered at glomerulus and passes into renal capsule - small components filtered
- Selective reabsorption - useful components of blood reabsorbed and waste filtered.
Explain the process of ultrafiltration
- High pressure in the glomerulus forces out water and small molecules of blood into renal capsule
- filtrate does not contain RBC or plasma proteins
Give two reasons for the high pressure within the glomerulus
- Diameter of afferent arteriole is bigger than diameter of efferent arterioles
- Coiled capillaries in glomerulus further restircted blood flow
Explain the atmosphere of the glomerulus during ultrafiltration
- Low solute potential (water lost and plasma proteins stay)
- high-pressure potential
- high water potential (forced out capillaries)
What is the environment of the renal capsule during ultrafiltration?
- high solute potential - no plasma proteins
- relatively high pressure potential - much fluids
- high water potential
What is the pathway of filtration?
Layers between glomerular and renal capsule
- Glomerular capillary endothelium - pores (fenestrations) between endothelium cells
- Basement membrane - very impermeable - only allow water, glucose, amino acids and not proteins (effective filter)
- Renal capsule epothelium - podocytes have large filtration sites.
What does the proximal convoluted tubule do?
means 85% filtrate reabsorbed
What does the distal convoluted tubule do?
- Final adjustments
- Toxic substances to be secreted into the filtrate
- water reabsorption
What is the collecting duct responsible for?
Water reabsorption
What is reabsorbed in the proximal convoluted tubule during selective reabsorption?
- Water - osmosis
- Ions - FD/AT
- Glucose - FD/AT
- Amino acids - FD/AT
- Small proteins
- urea - passive as waste
What adaptions has the proximal convoluted tubule made?
- Micorvilli from lumen to PCT
- Infoldings - PCT to Blood Vessel
- Mitochondria
What is the structure of the Proximal Convoluted Tubule?
- Lumen of PCT
- Cell of PCT
- Bloodstream
Explain the co-transport in selective reabsorption
- sodium ions actively transported from PCT cells into blood
- Blood carry sodium ions away
- Sodium ions diffuse into PCT cells from lumen of PCT by facilitated diffusion
- Glucose, amino acids or chlorine moved against conc. gradient using carrier protein and energy from FD
- Molecules diffuse from PCT into the blood.
What is the composition of filtrate after the PCT in selective reabsorption?
- 65% water and ions reabsorbed
- 100% glucose and amino acids reabsorbed
- Urea not selectively absorbed but some will passively diffuse due to the loss of water
- Conc. of urea increases.
What is the role of the Loop of Henle?
- Make medulla concentrated with ions
- lowering water potential
- promoting the reabsorption of water by osmosis in the collecting duct.
- Two limbs - descending (permeable to water) and ascending (impermeable)
- Allows water to be reabsorbed from collecting duct
What happens in the descending limb of the loop of henle?
- water leaves filtrate(reabsorbed)
- Sodium ions enter filtrate
- Permeable to water
What happens in the ascending limb of the loop of henle?
- Sodium ions leave filtrate
- IMpermeable to water
What happens in the collecting duct of the loop of henle?
- Water leaves the filtrate
- Reabsorbed
When is the filtrate most concentrated in the loop of Henle?
- The connection of ascending and descending limb
- Bottom of U
- Most ions nad least water
What section of the selective reabsorption process occurs in the Loop of Henle?
Explain the process
- Sodium ions actively transported out ascending limb
- Some sodium passively diffuse into descending majority accumulate in interstitial region (lower water potential)
- Water osmosis from descending to blood vessel
- Filtrate moves along descending becoming more concentrated
- Bottom of ascending sodium diffuses out
- Filtrate moves along ascending - sodium actively transported out
- Filtrate less concentrated and water potential more conc.
How does being longer effect the efficiency of the Loop of Henle?
- More efficient
- As deeper into the medulla so the water potential is lower and more can be reabsorbed.
What is the countercurrent multiplier in reference to selective reabsorption in the Loop of Henle?
- Filtrate in collecting duct with low water potential meets interstitial fluid with even lower water potential
- Ensures water potential gradient exists for the entire length of the collecting duct.
- Meaning more water can be reabsorbed
In what two ways does your body respond to being dehydrated?
- Release more anti-diuretic hormone - allows more water to be reabsorbed in DCT and collecting duct
- Increasing thirst - drink more water and so more water in blood.
What is ADH?
- Anti-diuretic hormone
- produced in hypothalamus
- Stored and secreted from posterior pituitary
How does ADH react to the water potential being too low?
- Osmoreceptors in the hypothalamus shrink
- Sends impulses to the posterior pituitary causing ADH to be released
- ADH passes into the blood and travels to the kidneys.
How does ADH work?
- Bind to receptors on cells of DCT and collecting duct
- Cause phosphorylase to be activated
- Causes vesicles within cell to move and fuse to cell surface membrane
- Vesicles contain pieces of plasma membrane and aquaporins which are inserted in the membrane
- Increase permeability of CD to water and urea
- More water into medulla fluid then BV by osmosis
- Urea into medulla fluid and lowers water potential allowing more water to be absorbed.
- Result - less urine produced.
How does the body make you feel thirsty?
Osmoreceptors send impulses to the thirst centre of the brain increasing the intake of water.
How does negative feedback work in response to water potential?
- More water is drunk and reabsorbed
- Water potential rises
- Osmorecpetors increase in size as water enters
- fewer impulses sent to posterior pituitary and thirst centre of brain
- Less ADH released and less water is drank
