Chp 6 - Homeostasis controing fluid & gas levels

Why is fluid so important inside the body?

Roles:

• transport substance around body

• Facilitate movement across membranes

• Site of chemical reactions

• ∴ Volume of water & concentration of dissolved substances controlled to remain within tolerance levels for body

What is intracellular and extra cellular fluid?

Intracellular: fluid inside cells (aka cytosol)

Extracellular: fluid outside cells

What are some extracellular fluids?

• blood plasma located within blood vessels

• → intravascular fluid

• Fluid between cells

• → interstitial fluid/ intercellular fluid/ tissue fluid

• Fluid in specific body regions

• → transcellular fluid (includes fluid in brain, spinal cord, eyes, & joints surround heart)

Are body fluids isolated from one another?

No.

• continuous exchange of materials between them.

What is osmotic concentration?

Concentration of solutes

• aka osmolarity

What is osmotic pressure?

• tendency of a solution to take in the pure solvent

• Fluid moves from areas of low concentration to high concentration.

• Greater osmotic concentration difference = greater osmotic pressure

How is body fluid obtained?

• water (through drinking or contained in food)

• By-product of chemical processes occurring within cells

• → metabolic water

How are body fluids lost?

• via kidneys, skin, surface of lungs, alimentary canal

• ~2.5L lost per day & 2.5L needs to be gained

Define excretion

• removal of waste products of metabolism from the body

Why must excretion take place?

• wastes are toxic, would be harmful to health if allowed to accumulate in boy fluids

• Every cell produces waste prices so removal before harmful concentration important

How are the lungs involved in excretion?

• excrete CO2

• CO2 & water produced by all body cells during cellular respiration

• Body cannot use CO2

• → carried in blood until reaches lung

• → where excreted

• Some water lost from lungs as water vapour when exhaled.

How are sweat glands involved in excretion?

• secrete water containing by-products of metabolism

• → salts, urea, lactic acid

How is the alimentary canal involved in excretion?

• alimentary canal passes bile pigments that enter end small intestine w bile

• → pigments breakdown products of haemoglobin from red blood cells

• Leave body w faeces

• → bulk of faeces composed of undigested food materials (not considered excretory products bcs not produced by cells)

How are they kidneys involved in excretion?

• kidney principle excretory organ

• Responsible for maintaining constant concentration of materials in body fluids

• Removes urea produced by liver from breakdown of proteins

Why do kidneys operate as an excretory organ and also regulate the composition of body fluids?

• remove excretory wastes/materials

• Only place where water loss can be regulated to achieve constant concentration of dissolved substances in body fluids

What and where are the kidneys located?

• pair of reddish-brown organs

• Located in abdomen

• On either side of vertebral column ~ level of lowest rib

• Attached to rear wall of abdominal cavity

What is attached to the kidneys?

Ureter (tube) leaves each kidney

→ drains into muscular reservoir

urinary bladder

→ empties to outside through

Urethra (tube)

What are the kidneys made up of?

1.2 million microscopic units called nephrons

→ functional unit of kidney

Cary out kidney’s role of excretion & water regulation

How does a nephron carry out its function? (LONG!)

• Blood enters glomerulus under high pressure

• Filtration: high blood pressure forces water & small dissolved molecules out of blood into capsule

• → large molecules & blood cells retained in blood

• Filtrate is collected by glomerular capsule

• Reabsorption: Filtrate passes through proximal convoluted tubule, distal convoluted tubule, collection duct

• → water & other useful substances reabsorbed into peritubular capillaries

What small molecules are lost in the glomerulus?

• Na, K, Cl, H ions

• glucose

• amino acids

• urea

What is reabsorbed at the proximal convoluted tubule?

• Glucose

• Amino acids

• Water

• Sodium

• Bicarbonate

• Potassium

• Calcium

• Phosphate

Through (Osmosis: water) (active) (simple) ASK!!

What happens to the osmotic pressure as water is lost?

• as after lost, plasma becomes more concentrated ∴ higher osmotic pressure

• → water moves from interstitial fluid into plasma by osmosis

• → ∴interstitial fluid more concentrated ∴ water diffuses out of cells

• → cells shrink from dehydration

How does the body counteract the shrinkage of cells?

• osmoreceptis in hypothalamus deco increased in osmotic pressure

• Number of responses triggered to increase water content

• And ∴ lower osmotic pressure

What type of reabsorption happens at the Proximal convoluted tubule & Loop of Henle?

-OSMOSIS

What type of reabsorption happens at the Distal convoluted tubule and collecting tubule/duct?

• ACTIVE REABSORPTION

What is the level of active reabsorption controlled by?

Hormone: Anti-diuretic hormone

→ produced by hypothalamus

→ released from posterior lobe of pituitary gland

How does ADH control active reabsorption in the kidneys?

• permeability of walls of distal convoluted & collecting duct controlled by ADH

What happens when ADH concentration is high in blood plasma? → because hormones travel through blood

• tubules very permeable to water

• → ∴ water able to leave tubule and enter surrounding capillary network

• Outward flow of water from fluid within tubules reduces its volume

• → ∴ increases concentration of materials remaining

What happens when ADH concentration is low in blood plasma?

• tubules not very permeable to water

• → ∴ little water reabsorbed into plasma of blood

• Fluid within tubules remains fairly dilute, as its volume not reduced to any significant extent

How is the action of ADH in controlling water balance displayed through a negative feedback loop? (VERY LONG & IN-DEPTH)

• Stimulus: The osmotic pressure of the blood is raised due to the decrease in water in the blood.

• Receptors: Osmoreceptors in the hypothalamus detect the increased osmotic pressure of the blood.

• Modulator: The hypothalamus stimulates the posterior lobe of the pituitary gland to release ADH

into the bloodstream.

• Effector: ADH is carried all over the body by the blood but it affects its target organs, which are

the nephron tubules in the kidney. The permeability to water of the distal convoluted tubules and

the collecting ducts is increased.

• Response: More water is then reabsorbed into the blood plasma from the distal convoluting

tubule and collecting duct.

• Feedback: The reabsorption of water increases the amount of water in the plasma and so the

osmotic pressure of the blood is decreased. This adjustment has eliminated or reduced the

original stimulus; a negative feedback has occurred.

How is the action of ADH in controlling water balance displayed through a negative feedback loop? (PICTURE, NOT IN-DEPTH)

What is aldosterone secreted by?

• adrenal cortex

Why is aldosterone secreted?

In response to:

• decrease in concentration of sodium ions in blood

• Decrease on blood volume

• Decrease in blood pressure

• Increase in concentration of K ions in blood

How does aldosterone play a part in regulating water output?

• acts on Distal convoluted tubules & convoluted ducts

• → to increase amount of Na ions reabsorbed into bloodstream

• → & amount of K secreted in urine

How are the effects of aldosterone achieved?

• through active transport using sodium-potassium pumps

Why does aldosterone have a role in regulating water content?

• 3 sodium ions reabsorbed = 2 potassium ions secreted

• ∴ Net movement of ions into blood

• →subsequent transport of water into blood via osmosis

How is a thirst response achieved?

• osmoreceptors stimulate thirst centre in hypothalamus

• → prompt person to drink water

What does drinking water achieve?

• fluid absorbed across wall of alimentary canal

• → into blood

• = decrease osmotic pressure

What would a thirst response look like through a negative feedback loop? (LONG & IN-DEPTH)

Stimulus: As water is lost from the various body fluids, there is a reduction in plasma volume and

an increase in osmotic concentration of the extracellular fluid.

• Receptor: Osmoreceptors in the thirst centre in the hypothalamus detect the rising osmotic

concentration of the blood. Other stimuli such as a dry mouth are also involved.

• Modulator: Stimulation of the thirst centre in the hypothalamus makes the person feel thirsty.

• Effector: The conscious feeling of thirst stimulates the person to drink.

• Response: The fluid consumed is absorbed from the alimentary canal into the plasma in the blood.

• Feedback: As the blood circulates through the body, it enables the interstitial fluid and intracellular

fluid to return to the normal osmotic concentration. After drinking, the thirst centre is no longer

stimulated and the desire to take in water ceases

What would a thirst response look like through a negative feedback loop? (IMAGE, NOT IN-DEPTH)

What is dehydration?

• whe. Water loss exceeds water intake

• → not enough water in body to carry out normal functions

• loose through: sweating, vomiting, diarrhoea etc

What are symptoms of dehydration?

• noticeable when person lost ~2% normal body water

• Severe thirst, low blood pressure, dizziness, headache.

• → if untreated = delirious, loose consciousness, may die

What is water intoxication?

• occurs when body fluids become diluted & cells take in water by osmosis

• → may happen if person loses a lot of water & salts through sweating, & replaces loss with plain water (should drink water containing dissolved substances)

What are some symptoms of water intoxication?

• lightheadedness

• Headache

• Vomiting

• Collapse may follow

What is cellular respiration?

What system & body part regulate gas concentrations

• respiratory system

• Lungs: exchange of CO2 & oxygen occurs

• → ∴changes in breathing change amt of oxygen taken in & amt of CO2 excreted

What system transports the gases around the body?

• circulatory system

• → oxygen from lungs to cells (used)

• → CO2 produced by cells to lungs (excretion)

• ∴ Circulatory system also involved in regulation of gas concentrations

What muscles control breathing?

• Diaphragm (muscle that separates thorax from abdomen)

• Intercostal muscles (muscles between ribs)

What do the diaphragm and intercostal muscles need to work?

• stimulation from nerve impulses to initiate contraction

→ spinal nerves

-. Origin in spinal cord @ level of neck & thorax

What nerve impulses is the diaphragm stimulated by?

• Phrenic nerves

What nerve impulses are the intercostal muscles stimulated by?

• intercostal nerves

What are phrenic and intercostal nerves controlled by?

• respirate centre

• → located in medulla oblongata

What are the 2 regions of the respiratory centre?

1. Controls expiration

2. Controls inspiration

→ coordinate breathing = messages pass back & forth between neurons in the 2 regions

Explain this equation

Oxygen & CO2 carried in blood

→ concentrations affect breathing rate & depth

Concentration of CO2 in blood plasm affects concentration of H ions

→ when CO2 dissolves in water = forms carbonic acid

→ breaks down readily to form H ions and bicarbonate ions

What are peripheral chemoreceptors?

• group of cells within walls of aorta & carotid arteries

• Sensitive to changes in concentration of oxygen, CO2, & hydrogen ions in blood plasma

• → known as aortic & carotid bodies

What are central chemoreceptors?

• located in medulla oblongata

• Sensitive it changes in concentration of CO2 in blood & hydrogen ions in cerebrospinal fluid

What happens when chemoreceptors are stimulated?

• send nerve impulses to area of respiratory centre that regulates breathing

How large is the effect of blood oxygen concentration on breathing rate?

If blood oxygen concentration is within a normal range than the effect on breathing rate is slight

→ needs to fall to very low levels to have major effect

What happens if there is a minor fall in blood oxygen concentrations?

• slight increase in breathing rate

What happens if there is a large fall in blood oxygen concentrations?

• detected by peripheral chemoreceptors (aortic & carotid bodies)

• Nerve impulses transmitted to respiratory centre in medulla oblongata

• Nerve impulses stimulate transmission of messages to diaphragm and intercostal muscles

• → to contract

• = breathing rate & depth increases

How large is the effect of blood CO2 concentrations on breathing rate?

Small increase in CO2 marks increase in rate of breathing

Very strong.

What is the association between CO2 ions and H ions?

concentration of carbon dioxide in the plasma is associated with the concentration of hydrogen ions.

(CO2 ions directly affect hydrogen ions)

What happens when there is an increase in CO2 & H ions blood concentration?

• results in stimulation of central & peripheral chemoreceptors

• → nerve impulses transmitted to respiratory centre in medulla oblongata

• Neurons making up central chemoreceptors seperate from (but still communicate) with neurons in respiratory centre

• Response takes several minutes

• 70-80% in breathing rate

What causes an immediate increase in breathing rate following an increase in CO2?

• stimulation of peripheral chemoreceptors (aortic & carotid bodies)

• → due to increase in H

Where are chemoreceptors most sensitive to changes in CO2 located?

• Plasma in medulla oblongata

How does H ion concentration affect the breathing rate?

• as H increases, pH decreases

• → ∴ breathing rate increases

• Decrease in pH stimulates peripheral chemoreceptors (aortic and carotid bodies) (in aorta & carotid artery’s)

• Nerve impulses transmitted to respiratory centre (in medulla oblongata)

• ∴ Breathing rate increased

If breathing is done voluntarily, what happens?

• voluntary control comes via connections from cerebral cortex to descending tracts in spinal cord

• ∴ Bypasses respiratory centre in medulla oblongata

• Protective device as enables us to prevent irritating gases and water from entering lungs

What is hyperventilation?

• rapid, deep breathing

• → provide more Oxygen than required

• → remove more CO2 than necessary

• Can occur voluntarily or stimulated b physical stress (severe pain/emotional)

What happens if a person hyperventilates?

• usually corrects itself

• → bcs reduction in CO2 means chemoreceptors are not stimulated

• → reducing rate & depth of breathing until CO2 levels return to normal

When can hyperventilation become dangerous?

• before swimming underwater

• → person longer underwater not because more oxygen but bcs loss of CO2

• Individual may loose consciousness from lack of oxygen before brain feels urge to breathe