What is homeostasis?
The body's ability to maintain relative stability in its internal environment despite external changes.
What must a multicellular organism consistently maintain to survive?
The composition of its internal environment, including blood, lymph, and interstitial extracellular fluid.
What is the regulation of a multicellular organism’s internal fluid composition called?
Osmoregulation.
What happens to a cell in a hypertonic solution?
Water leaves the cell, dehydrating it.
How does an isotonic solution compare with a cell’s solute concentration?
It has the same solute concentration.
What happens to a cell in a hypotonic solution?
Water enters the cell, causing it to swell and possibly burst.
What are the five components of a homeostatic control system?
A stimulus, a controlled variable, a receptor, a control centre, and an effector with its response.
What message do homeostatic receptors send after detecting a parameter or its change?
A nerve or hormonal message.
Which three receptor types are listed in homeostatic control?
Thermoreceptors, baroreceptors, and chemoreceptors.
How does a homeostatic control centre determine effector activity?
It compares received information with a set point and uses the deviation to determine effector activity and compensation intensity.
How does a homeostatic effector help restore balance?
It acts on the regulated parameter.
How does the nervous system communicate with different parts of the body?
Through neurons and synaptic spaces.
How quickly can nervous-system impulses propagate?
With delays of about a second or less.
How does the endocrine system transport hormones to tissues?
Through the blood and then interstitial fluid.
Where do peptide hormones act, and how quickly can they act?
At the cell membrane, within minutes.
Where do steroid and thyroid hormones act, and how long may they take?
At target-cell DNA, from a few hours to a few months.
How does negative feedback affect a changing variable in homeostasis?
It returns the variable toward a new dynamic equilibrium.
What does an initial perturbation trigger in positive feedback?
A response that amplifies the perturbation.
Until what event can positive feedback continue amplifying a disturbance?
Until the initial disturbance disappears.
What do the kidneys filter from the blood?
Metabolic waste.
Which variables besides waste removal do the kidneys regulate?
Water balance, pH, and blood concentrations of sodium, potassium, bicarbonate, and calcium ions.
Which two hormones chiefly regulate urinary excretion according to intake and losses?
Aldosterone and vasopressin (ADH).
Where are aldosterone and vasopressin produced, and how is vasopressin released?
Aldosterone is synthesized by the adrenal cortex; vasopressin is produced by the hypothalamus and released by the pituitary.
Which ion is most abundant in extracellular fluid?
Sodium.
What is the dietary source of sodium?
Dietary sodium chloride.
How does water respond when the kidney reabsorbs sodium?
Water follows sodium by osmosis.
What does ADH do when the body needs water?
It increases water permeability in the distal tubule and collecting duct.
How do alcohol and caffeine affect ADH and urine water excretion?
They inhibit ADH and increase water excretion in urine.
What triggers kidney renin release in the aldosterone pathway?
Blood volume and pressure that are too low for glomerular filtration.
How does aldosterone increase blood volume and pressure?
It increases sodium reabsorption, while chloride and water follow passively.
What reversible buffer reaction regulates blood pH?
What is the approximate pH of healthy blood?
About 7.4.
What is the average pH of urine?
Approximately 6.6.
What pH range can urine have?
From 4.5 to 8.
What happens to breathing when blood becomes acidic?
Breathing increases, shifting the buffer reaction toward carbon dioxide production for exhalation.
Which hormone do the kidneys secrete to stimulate red blood cell production?
Erythropoietin (EPO).
When is a person considered healthy in terms of internal balance?
When they maintain balance among internal functions and satisfy needs while keeping a stable internal balance.
Why does homeostatic compensation leave a small deviation from the set point?
The deviation is necessary to maintain regulatory compensation.
Where are dogs’ few eccrine sweat glands mainly located?
In their paw pads.
How do dogs primarily cool themselves?
By panting, which evaporates water from the tongue, and by vasodilation.
What does cortisol bind to in liver cells during prolonged stress?
Receptors.
What does cortisol activate after binding to DNA during prolonged stress?
Genes that increase glucose release.
How is positive feedback generally associated with disease or extreme change?
It is generally associated with disease or extreme change.
How does positive feedback initially affect stability?
It does not initially promote stability.
Which phenomena are governed by positive feedback?
Relatively infrequent phenomena.
Which receptors initiate predictive thermoregulation before body temperature changes?
Thermal receptors in the skin.
Which responses do skin receptors trigger in predictive thermoregulation?
Responses in skeletal muscles and blood vessels that reduce heat production and heat loss.
How many nephrons does each kidney contain approximately?
About one million.
Where are the nephrons located within each kidney?
In the cortex and medulla.
How do the kidneys protect substances needed for normal body function?
They prevent their loss in urine.
What are electrolytes?
Chemical elements that dissociate into ions when dissolved in water.
How does aldosterone affect kidney potassium and sodium handling?
It promotes potassium excretion and sodium retention.
Which hormone do parathyroid glands release when blood calcium falls below normal?
Parathyroid hormone (PTH).
What kidney product does PTH stimulate when blood calcium is low?
Calcitriol, the active form of vitamin D.
What does calcitriol promote in the digestive tract?
Calcium absorption.
What vitamin production do the kidneys activate in the skin?
Vitamin D production.
Answer 22 questions on Homeostasis and Kidney Regulation.
1. What does homeostasis enable the body to do despite changes in the external environment?
2. What is the term for regulating the composition of internal fluids such as blood, lymph, and interstitial fluid?
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