7.23 Homeostasis & Physiology

These flashcards cover the lecture’s key concepts on homeostasis, feedback loops, thermoregulation, blood glucose control, osmoregulation, oxygen regulation, hormonal pathways, and differences between ectotherms and endotherms.

What is the definition of homeostasis in physiological systems?

The maintenance of a relatively constant internal environment (e.g., pH, blood sugar, temperature) despite external changes.

Which two body systems are primarily responsible for coordinating homeostatic responses?

The nervous system and the endocrine (hormonal) system.

In a typical negative-feedback loop, name the four main components in order.

Stimulus → Receptor (sensor) → Control Center (e.g., hypothalamus, pancreas) → Effector (muscles, glands, blood vessels).

How does negative feedback differ from positive feedback?

Negative feedback reverses a change and returns the variable to a set point, whereas positive feedback amplifies the change until a specific endpoint is reached.

Give one classic physiological example of positive feedback.

Childbirth: cervical stretch triggers oxytocin release, intensifying uterine contractions until the baby is delivered.

Which brain region sets the temperature set-point and controls thermoregulation?

The hypothalamus.

During cold exposure, what two effector responses does the hypothalamus trigger?

Vasoconstriction of peripheral blood vessels and shivering in skeletal muscles.

During heat exposure, which two effector responses cool the body?

Vasodilation of skin blood vessels and activation of sweat glands (evaporative cooling).

Define ectotherm and give one animal group example.

An organism that depends largely on external environmental heat to regulate body temperature; e.g., reptiles, amphibians, most fish.

Define endotherm and state one consequence for metabolic rate.

An organism that generates internal heat to maintain body temperature; this requires a higher metabolic rate (e.g., mammals, birds).

Which two pancreatic hormones regulate blood glucose, and in which direction does each act?

Insulin lowers high blood glucose; glucagon raises low blood glucose.

Describe insulin’s primary action in the liver.

It stimulates conversion of glucose to glycogen for storage, lowering blood glucose levels.

Describe glucagon’s primary action in the liver.

It stimulates breakdown of glycogen to glucose, releasing glucose into the bloodstream and raising blood glucose levels.

Differentiate Type 1 and Type 2 diabetes in one sentence.

Type 1 involves insufficient insulin production (often autoimmune), while Type 2 involves decreased cellular sensitivity to insulin (often diet-related).

Which hormone is released by the kidney during low-oxygen conditions, and what is its target?

Erythropoietin (EPO); it targets bone marrow to increase red blood cell production.

Why do high-altitude athletes or blood dopers seek elevated erythropoietin levels?

More red blood cells raise oxygen-carrying capacity, enhancing endurance performance.

Name the two main adrenal ‘fight-or-flight’ hormones and list two physiological effects.

Epinephrine (adrenaline) and norepinephrine; they increase heart rate, elevate blood glucose, and stimulate skeletal muscle blood flow.

What hormone controls water reabsorption in kidney collecting ducts?

Antidiuretic hormone (ADH, also called vasopressin).

How does ADH conserve body water at the nephron?

It inserts aquaporin channels into the collecting-duct membrane, increasing water reabsorption into the bloodstream and producing concentrated urine.

Explain why caffeine or alcohol can cause dehydration.

They act as diuretics, inhibiting ADH action, so less water is reabsorbed and more dilute urine is produced.

What structural protein channels shift within the collecting-duct membrane to regulate water permeability?

Aquaporins.

Define stimulus, receptor, control center, and effector using body temperature as the example.

Stimulus: external heat/cold; Receptor: thermoreceptors in skin; Control Center: hypothalamus; Effector: sweat glands & blood vessels (heat) or muscles & blood vessels (cold).

At what approximate pH must human blood be maintained, and how is it stabilized?

Around pH 7.3–7.4, stabilized by chemical buffer systems (bicarbonate, proteins, phosphate).

What happens to hypothalamic signaling once a variable (e.g., body temp) returns to its set point?

Negative feedback stops further signaling—effectors turn off until the next deviation occurs.

Which feedback type resembles a household thermostat and why?

Negative feedback—because the system turns off the heater/AC once the set temperature is restored.

Identify one receptor location (besides skin) that can detect changes requiring homeostatic response.

Examples: heart, blood vessels, kidneys, pancreas—specific to the variable being monitored.

Why must endotherms have efficient circulatory and respiratory systems?

Their higher metabolic rate and internal heat production demand rapid oxygen delivery and waste removal.

Which hormone family diffuses through cell membranes and binds intracellular receptors, and why?

Steroid hormones (e.g., testosterone, estrogen) because they are non-polar and lipid-soluble.

Why do peptide (amino-acid-based) hormones need membrane receptors?

They are polar and cannot readily cross the lipid bilayer, so they bind to specific protein receptors on the cell surface to trigger signaling cascades.