Human Phys Exam 3

What distinguishes endocrine glands from exocrine glands?

Endocrine glands release hormones into interstitial fluid and blood; exocrine glands secrete substances into ducts

What are the three major chemical classes of hormones?

Steroid/lipid hormones, protein/peptide hormones, and amine hormones

What are five examples of steroid hormones?

Estradiol,testosterone, cortisol, aldosterone, and progesterone

What are five examples of protein/peptide hormones?

FSH, LH, ACTH, oxytocin, and ADH

What are four examples of amine hormones?

Epinephrine, norepinephrine, dopamine,, and thyroxine (T4)

What are steroid hormones synthesized from?

Cholesterol, which is converted into different steroid hormones by tissue-specific enzymes

How are protein hormones syntehsized?

They are synthesized from amino acids. Their specific three-dimensional structure is important for receptor binding.

Which neurohormones are synthesized by hypothalamic neurons?

ADH (vasopressin) and oxytocin

How do hydrophilic hormones produce their effects?

They bind to receptors on the plasma membrane because they cannot readily cross the lipid bilayer.

What are four examples of steroid hormones?

Oxytocin, FSH, ACTH, and LH

How do lipophilic steroid hormones produce their effects?

They cross the plasma membrane, bind intracellular receptors, and generally alter gene expression

What are four examples of lipophilic steroid hormones?

Estradiol, cortisol, progesterone, and testosterone

Why do only certain cells respond to a hormone?

Only target cells with the appropriate receptors can respond to that hormone. Sometimes called the molecular handshake

Are steroid hormones stored before secretion?

Generally, no. Steroid hormones are usually secreted as they are synthesized

What are the three possible fates of a secreted hormone?

It can bind to a target-cell receptor and produce a response, be metabolically inactivated, or be cleared and excreted

What determines the concentration of a hormone is plasma?

The balance between its secretion rate and clearance rate

How do hydrophilic and lipophilic hormones typically circulate in blood?

Protein hormones and many catecholamines circulate freely dissolved in plasma, while steroid hormones and some catecholamines bind to carrier proteins

What are three examples of hormone carrier proteins?

Albumin, sex hormone-binding globulin (SHBG), and transcortin (cortisol-binding globulin)

How does binding to carrier proteins affect hormones?

Carrier proteins generally increase hormone half-life. The free, unbound hormone is usually the biologically active fraction

What is the difference between receptor ip-regulation and down-regulation?

Up-regulation increases receptor number or sensitivity, while down-regulation decreases receptor number or sensitivity

What is an example of receptor down-regulation?

Prolonged exposure to high insulin concentrations may decrease the number of cell-surface insulin receptors

What is a recepto agonist?

A substance that binds to and activates a receptor, producing a biological response

What is a receptor antagonist?

A substance that blocks or opposes a hormone’s action. For example, tamoxifen acts as an estrogen antagonist in breast tissue

What is intracrine signaling?

A hormone precursor is converted into an active hormone that acts within the same cell

What are two examples of intracrine hormone conversion?

DHEA can be converted locally into estradiol or DHT, and testosterone can be converted into DHT by 5α-reductase in prostate cells

What is hormonal permissiveness?

One hormone allows another hormone to produce its full effect. For example, thyroid. hormone increases adipose-cell responsiveness to epinephrine

What is hormonal synergism?

Two or more hormones produce a combined effect greater than the sum of their individual effects, such as glucagon, epinephrine, and cortisol increasing blood glucose

What is hormonal antagonism?

Two hormones producing opposing affects, such as progesterone opposing estrogen action on the myometrium

What is a tropic hormone?

A hormone that regulates the secretion of another hormone

What is a trophic hormone?

A hormone that promotes secretion and the growth or maintenance of its target endocrine gland

How does TSH act as both a tropic and trophic hormone?

TSH stimulates thyroid follicular cells to produce T3 and T4 and promotes thyroid gland growth

How can prolonged elevation of TSH cause a goiter?

Sustained TSH stimulation promotes thyroid enlargement, which may occur in iodine deficiency

How does ACTH act as both a tropic hormone and trophic hormone?

ACTH stimulates cortisol and DHEA secretion from the adrenal cortex and maintains adrenal cortical tissue

What happens to the adrenal cortex when ACTH is chronically elevated or suppressed?

Excess ACTH can cause adrenal cortical hypertrophy, while chronically suppressed ACTH can cause atrophy of the zona fasciculata and zona reticularis

What connects the hypothalamus to the pituitary gland?

The infundibulum. The anterior pituitary is glandular tissue, while the posterior is neural tissue

Desrice the pathway connecting the hypothalamus and anterior pituitary.

Hypothalamic releasing or inhibiting hormones enter capillaries in the median eminence, travel through the hypophyseal portal veins, enter the anterior pituitary capillary bed, and regulate anterior pituitary hormone secretion

Which hormones are secreted by anterior pituitary acidophils?

Growth hormone (GH) and prolactin

Which hormones are secreted by anterior pituitary basophils?

ACTH, FSH, LH, and TSH

How does dopamine regulate prolactin secretion?

Dopamine tonically inhibits prolactin secretion, while TRH and VIP can simulate itH

How are posterior pituitary hormones syntehsized and released?

ADH and oxytocin are synthesized by hypothalamic neurons, transported down their axons, and released into the blood from the posterior pituitary

What are the primary functions of ADH and oxytocin?

ADH promotes water conservation by the kidneys, while oxytocin stimulates uterine contractions and milk ejection

What is short-loop negative feedback?

An anterior pituitary hormone inhibits the release of hypothalamic hormone. For example, GH can inhibit GHRH

What is a long-loop negative feedback?

A peripheral hormone inhibits hormone release from the pituitary and/or hypothalamus. Examples include thyroid hormones, cortisol, and IGF-1

Describe the hypothalamic-pituitary-thyroid (HPT) axis.

Hypothalamus releases TRH → anterior pituitary releases TSH → thyroid releases T3 and T4. Thyroid hormones negatively regulate TRH and TSH

What happens to TRH, TSH, and thyroid hormones during primary thyroid failure?

T3 and T4 decrease, reducing negative feedback and causing TRH and TSH to increase. Prolonged TSH stimulation may enlarge the thyroid.

Describe the hypothalamic-pituitary-adrenal (HPA) axis.

Hypothalamus releases CRH → anterior pituitary releases ACTH → adrenal cortex releases cortisol. Cortisol negatively regulates CRH and ACTH

What happens to cortisol and ACTH during primary adrenal cortical failure?

Cortisol decreases, while CRH and ACTH increase because negative feedback is reduced

What happens when the pituitary gland does not produce enought ACTH?

Cortisol secretion decreases, and the ACTH-dependent adrenal cortex may undergo atrophy

How does prolonged use of exogenous cortisol affect the HPA axis?

It suppresses CRH and ACTH secretion through negative feedback, potentially causing adrenal cortical atrophy

How does chronic stress affect the HPA axis?

Stress activates the HPA axis, increasing ACTH stimulation and cortisol secretion

Describe the growth hormone-IGF-1 axis.

Hypothalamic GHRH stimulates anterior pituitary GH release → GH stimulates the liver and other tissues to produce IGF-1. IGF-1 provides long-loop feedback, while GH provides short-loop feedback

What is the difference between primary and secondary endocrine hypersecretion?

Primary hypersecretion originates in the peripheral endocrine gland, while secondary hypersecretion originates upstream, such as the pituitary gland

Which hypothalamic hormones stimuate and inhibit GH secretion?

GHRN stimulates GH secretion, while somatostatin (GHIH) inhibits it

How is growth hormone normally secreted?

GH is released from anterior pituitary somatotrophs in a pulsatile pattern influences by circadian rhythms

What are the direct metabolic effects of growth hormone?

GH promotes fatty acid release and increases glucose availability

How does IGF-1 contribute to the effects of GH?

GH stimulates IGF-1 production in the liver and other tissues. IGF-1 mediates much of GH-induced tissue growth and cell proliferation

What is the difference between gigantism and acromegaly?

Excess GH before epiphyseal plate fusion causes gigantism, while excess GH after fusion causes acromegaly, characterized by enlarged hands, feet, bones, and soft tissues

What stimulates parathyroid hormone (PTH) secretion?

Decreased plasma calcium stimulates parathyroid chief cells to release PTH. As calcium rises, PTH secretion decreases through negative feedback

How does PTH increase blood calcium levels?

PTH promotes calcium release from bone, increases kidney calcium reabsorption, and stimulates calcitriol production, which increases intestinal calcium absorption

What are the consequences of hypoparathyroidism?

Low PTH causes hypocalcemia, which can lead to tetany, carpopedal spasms, laryngospasm, and cardiac arrhythmias

What are the conseqeunces of hyperparathyroidism?

Excess PTH can cause hypercalcemia, bone weakening, and kidney stones

Why is the left ventricular wall thicker than the right?

The left ventricle pumps blood into the high-pressure systemic circulation, requiring greater force. The right ventricle pumps into the lower-pressure pulmonary circulation

How do the stroke volumes of the left and right ventricles compare?

Both ventricles pump approximately the same stroke volume over time, even though they generate different pressures

What is the basic equation for blood flow?

Blood flow (F) = pressure gradient (ΔP) / resistance (R)

How do pressure gradient and resistance affect blood flow?

Increasing the pressure gradient increases blood flow, while increasing resistance decreases blood flow

What three factors determine vascular resistance?

Vessel radius, vessel length, and blood viscosity. Vessel radius has the greatest influence because resistance is inversely proportional to the fourth power of radius

What happens to vascular resistance if the radius of a vessel is reduced by half?

Resistance increases 16 fold, assuming other factors remain constant

Which blood vessels primarily control total peripheral resistance (TPR)?

Arterioles, because their smooth muscle can constrict or dilate to regular resistance

What is the relationship between mean arterial pressure (MAP), cardiac output (CO), and total peripheral resistance (TPR)?

MAP = CO x TPR, assuming right atrial pressure is negligable

What does the P wav represent on an ECG?

Atrial depolarization, which is followed by atrial contraction

What does the QRS complex represent on an ECG?

Ventricular depolarization, which initiates ventricular contraction. Atrial repolarization occurs during this time but is usually hidden by the QRS complex

What does the T wave represent on an ECG?

Ventricular repolarization, which is followed by ventricular relaxation

Does the electrical activity or mechanical contraction occur first in the cardiac cycle?

Electrical activity, depolarization precedes contraction, and repolarization precedes relaxtion

How long does one cardiac cycle last at a heart rate of 75 beats per minute?

~ 0.8 seconds

What are the approximate durations of atrial systole, ventricular systole, and ventricular diastole?

At 75 bpm, atrial systole lasts about 0.1 seconds, ventricular systole lasts 0.3 seconds, and ventricular diastole lasts 0.4 seconds

What happens during atrial systole?

The atria contract and push the remaining blood into the ventricles, completing ventricular filling before ventricular systole

Which heart valves are open during ventricular filling (diastole)?

AV valves (mitral and tricuspid) are open, semilunar valves are closed

What causes the first heart sound (S1)?

Closure of the AV valves at the beginning of ventricular systole

What occurs during isovolumetric ventricular contraction>

The ventricles begin contracting while all heart valves are closes. Ventricular pressure increases, but ventricular volume remains constant

When do the semilunar valves open?

When ventricular pressure exceeds the pressure in the aorta or pulmonary trunk, allowing blood to be ejected from the ventricles

What causes the second heart sound (S2)?

Closure of the aortic and pulmonary semilunar valves at the end of ventricular ejection

What occurs during isovolumetric ventricular relaxation?

The ventricles relax while all valves are closed. Ventricular pressure decreases, but ventricular volume remains constant.

When do the AV valves reopen?

When ventricular pressure decreases below atrial pressure, allowing blood to flow from the atria into the ventricles

What is end-diastolic volume (EDV), and how does it related to preload?

EDV is the amount of blood in a ventricle immediately before contraction. It is closely related to preload, which describes ventricular muscle stretch before contraction

What is end-systolic volume?

The amount of blood remaining in a ventricle after ventricular contraction and ejection

How is stroke volume calculated?

SX = EDV - ESV

How is ejection fraction (EF) calculated, and what does it indicate?

EF = (SV/EDV) x 100%

It represents the percentage of ventricular blood ejected with each contraction. A typical mean EF is ~ 63-60%, an EF of 40% indicates markedly reduced pumping fraction

What is valvular stenosis?

A condition in which a heart valve fails to open completely, restricting forward blood flow and increasing the workload on the heart

How does mitral valve stenosis affect blood flow?

It restricts blood flow from the left atrium into the left ventricle during diastole

How does aortic valve stenosis affect blood flow?

It restricts blood flow from the left ventricle into the aorta during systole

What is valvular regurgitation?

A condition in which a heart valve fails to close completely, allowing blood to flow backward

When does mitral regurgitation occur, and in which direction does blood flow?

During ventricular systole, blood flows backward from the left ventricle into the left atrium

When does aortic regurgitation occur, and in which direction does blood flow?

During ventricular diastole, blood flows backward from the aorta into the left ventricle

How is cardiac output (CO) calculated?

CO = heart rate (HR) x stroke volume (SV). Resting CO is about 5.6 L/min for a 70kg person

What happens to cardiac output during exercise?

Cardiac output increases because heart rate, stroke volume, and venous return increase to meet the greater oxygen demands of active tissues

How does hemorrhage initially affect cardiovascular function?

Blood loss decreases circulating blood volume, venous return, EDV, stroke volume, cardiac output, and mean arterial pressure

How does the sympathetic nervous system compensate for hemorrhage?

It increases heart rate and total peripheral resistance through sympathetic stimulation. helping maintain arterial blood pressure

What does “juggling resistance” mean during exercise?

Blood flow is redistributed toward active skeletal muscles and away from less immediately essential organs, such as the kidneys and digestive tract

What happens when epinephrine binds to β2-adrenergic receptors in skeletal muscle arterioles?

The arterioles dilate, decreasing vascular resistance and increasing blood flow to active skeletal muscles

What happens when catecholamines activate α1-adrenergic receptors in renal and digestive arterioles?

The arterioles constrict, increasing resistance and decreasing blood flow to the kidneys and digestive organs