IB Biology HL: D3.3 - Homeostasis

homeostasis

maintenance of internal environment of the internal environment of an organism at preset values despite fluctuations due to external factors

homeostatic factors

• body temperature

• blood glucose concentration

• blood ph

• blood osmotic concentration

What type of feedback loop are used for homeostasis

negative feedback loop (not positive): returns homeostatic variables to the set point from values above and below the set point.

blood glucose concentration

• too much glucose: insulin

• too little glucose: glucagon

secreted by pancreatic endocrine cell

exocrine glands

glands which releases products into ducts, not blood level

pancreas

releases insulin (beta cells) and glucagon (alpha cells). Endocrine glands which secrete into bloodstream.

8 Marker blood sugar Homeostasis

• individual eats

• stimulus: causes glucose spike in blood

• detected by islets of langerhans pancreas

• beta cells produce and release insulin hormone n bloodstream

• cells uptake more glucose as they embed more GLUT4 receptors on their surface

• stored as glycogen

• blood glucose level decreases

• detected by islets of langerhans

• alpha cells produce glucagon and release it

• liver breaks down glycogen stores bc of glucagon

• blood glucose level rises, closer to optimum

compare negative and positive feedback

• positive: amplifies initiating stimuli - move system away from starting state: FSH, stimulate follicle growth, stimulating follicle developmenr

• negative: counteract changes from set target value: keeps within narrow limits

requires energy, but is needed

example of positive feedback

• As the pregnancy approaches the end, the growing foetus’s head applies pressure against the cervix.

• The increased pressure stretches the cervix wall and stimulates the nerves. These nerves inform the hypothalamus, which stimulates the pituitary gland.

• The pituitary gland releases the hormone oxytocin.

• Oxytocin travels to the uterus and stimulates it to contract.

• The contraction of the uterus pushes the foetus to the cervix, which causes more pressure on the cervix wall.

• This pressure causes the nerves to stimulate the pituitary gland to release more oxytocin.

Negative feedback in regulation of blood glucose

• blood sugar level rises

• stimulates beta cells in islets of Lagerhans

• causes secretion of insulin

• promotes liver and muscle cells to bring GLUT4 receptors on the cell membrane, take in glucose and store it as glycogen

• blood sugar falls

• stimulates alpha cells in islets of lagerhans

• secrete glucagon

• causes liver and muscle to break down glycogen and release it as glucose

glucagon

acts as a chemical messenger

it activates enzymes in the liver and other glycogen storage sites

as well as converting amino acids into glucose

glucose is released into bloodstream

why does hyperglycemia increase blood pressure

• increases glucose

• greater osmotic effect

• lower water potential, more water goes in bloodstream

diabetes

• consistently elevated blood glucose levels, which can cause damage to tissues

• chronic

• leads to the presence of glucose in urine, dehydration

diabetes symptons

• excessive thirst

• excessive hunger

• unexplained weight loss

• blurred vision

• slow wound healing

• fatigue

• frequent urination

name of endocrine glands of pancreas

Islets of Langerhans

type 1 diabetes

• caused by insufficient$ or no insulin production

• caused by autoimmune destruction of beta cells of pancreatic islet

• often sudden and in childhood

type 1 diabetes treatment

insulin therapy: insulin taken when is needed

type 2 diabetes causes

• deficiency of insulin receptors

• or receptors are desensitised, because of excessive insulin

• gradual condition, insulin resistance

type 2 diabetes treatment

• reduction in weight

• increase in physical activity

• medications such as medformine

• family history

endotherms

generate heat internally to maintain a steady body temperature ( mammals, birds)

ectotherms

rely on external heat sources to regulate body temperatures ( reptiles, fish)

thermoregulation

control/maintenance of core body temperatures to keep them close to a set point

how do endotherms control internal temperatures

• peripheral thermoreceptors send signals to hypothalamus

• hypothalamus relases thyrotropin stimulating hormone (TSH)

• activates pituitary gland to release thyroid stimulating hormone

• which stimulates thyroxin production in the thyroid gland

• thyroxin causes brown tissue to generate heat

• increases metabolic rate

thyroxin functions

brown adipose tissue

type of adipose tissue which can generate heat at a fast rate: babies have more than adults.

uncoupled respiration

when respiration is done without producing atp, just to produce heat

osmoregulation

The regulation of the body's water balance and solute concentration to maintain homeostasis.

role of kidneys

• regulation of water and ion balance (osmoregulation)

• removal of toxins and metabolic waste products (excretion)

units for osmotic concentration

osmoles per litre (osmol L¹)

different excretory products for different organisms

ammonia for fish

urea for mammals

uric acid for birds

excretion

removal of toxic waste products from the metabolism from the body.

all parts of a kidney

medulla kidney

site of reabsorption of water

renal pelvis

collecting ducts deliver urine to the pelvis to be passed onto the ureter

renal vein

collects filtered from from kidney

renal artery

delivers oxygen rich blood to the kidney

ureter

carries urine to the bladder

cortex

ultrafiltration and selective re-absorption of blood content

Nephrons

The functional unit of the kidney that filters blood, reabsorbs useful substances and excretes waste products in the form of urine. There are millions of them

parts of a nephron

where does blood come in and out of a nephron

comes in an afferent artery and out an efferent artery

parts of nephron, in cirtex or medulla

cortex: bowman’s capsule, proximal convoluted tubule

medulla: loop of henley, collecting duct

process of ultrafiltration

blood enters thought a larger afferent artery, and smaller efferent artery

glomerulus is a zone of a high pressure capillary bed

forces ultrafiltration, water and small molecules are forced out and enters bownman’s capsule as capillary walls are fenestrated

after go to the proximal convoluted tubule, where things that are needed (salts…) are reabsorbed into the blood by active transports

structural adaptations of bowman capsule

• podocytes: cells of the inner walls of the bowman’s capsule with feet-like extensions which wrap around like arterioles. Small gaps allows most filtrate to pass through

• fenestration: tille holes in endothelim of capillaries, which allows molecules and fluids to leave plasma

• basement membrane: surrounds and supports the capillart wall. It is made of a gel of negatively charged glycoproteins, which forms a mesh

proximal convoluted tubule

• contain microvilli to increase SA

• actively transports glucose and salt into blood

• water and Chloride are passively following a transport gradient

• absorbs that stuff inside it

• puts that stuff back into bloodstream

loop of henle

• occurs after proximal tubule

• descending loop is permeable to water, so water osmoses out of descending limb as medulla is salty

• ascending loop isn’t, but actively transports salt ions (na and cl), so decreases water potential, so in descending loop water osmoses out

• countercurrent system: blood and fluid go in opposite directions

  

distal convoluted tubule

Fine adjustment of PH

anti diurectic hormones

ADH

amount of water to be released from the collecting ducts to be retained by body is dependent of ADH. Controls how many aquaporins are present, ie how much water can passively transport into the cell membrane of collecting ducts