Phys IV

Describe how hormones are synthesized

Hormones are chemical messengers synthesized and secreted by specialized endocrine glands directly into the bloodstream to regulate distant target organs.

What are the three major classes of hormones?

• Peptide/Protein Hormones: Chains of amino acids.

• Steroid hormones (such as cortisol, aldosterone) are produced from cholesterol by the adrenal cortex and the gonads and from steroid precursors by the placenta.

- Aldosterone and cortisol are produce by the adrenal cortex.

- Estradiol and progesterone are produce mainly in the ovaries.

- Testosterone is produce mainly by the testes.

• Amine hormones such as dopamine are amino acid derivatives. Examples: 

-Thyroid hormones

-Catecholamines (such as epinephrine): secreted by the adrenal medulla and the hypothalamus

What class of hormone do epinephrine, dopamine, insulin, cortisol, and aldosterone belong to?

• Epinephrine: Amine hormone

• Dopamine: Amine hormone

• Insulin: Peptide/Protein hormone.

• Cortisol: Steroid hormone

• Aldosterone: Steroid hormone

How is Cortisol made in the adrenal cortex?

When cortisol levels drop or the body faces stress, the hypothalamus releases corticotropin-releasing hormone (CRH)

• Anterior pituitary gland receptor binding causes ACTH to release

• The activated receptors cause G protein bound to GDP and convert it to GTP.

• The alpha and beta subunits of the GTP dissociate, and the G protein activates adenylyl cyclase.

• Adenylyl cyclase catalyzes the conversion of ATP to cAMP.

• cAMP activates (PKA), which phosphorylates various proteins, converting them into phosphoproteins.

• Cholesterol undergoes several enzymatic conversions within the cell, driven by the protein phosphorylation, to produce cortisol.

• Negative feedback: inhibits ACTH and CRH release

Describe how hormones are transported

Hormones are transported through the bloodstream either dissolved in plasma or bound to carrier proteins

On the target organ (tissue or cell) where is the receptor located for catecholamine? Steroid?

-Located on the outer surface of the cell membrane (plasma membrane) because these hormones are water-soluble and cannot cross the lipid bilayer.

-Located inside the cell (in the cytoplasm or nucleus) because these lipid-soluble hormones easily diffuse directly through the plasma membrane

Which type of hormones last in the blood stream for long periods of time (hours to

days)?

Steroid and thyroid hormones because they are bound to plasma carrier proteins, which shields them from rapid degradation and excretion.

How are hormones removed from the bloodstream?

1. The liver and kidneys remove hormones from the plasma by metabolizing or excreting them. 

• Peptide hormones and catecholamines are soluble in plasma and are rapidly removed from the blood. 

• Steroid and thyroid hormones are poorly soluble; mostly bound to plasma proteins and are removed more slowly, mainly because they circulate bound to plasma proteins.

How does the anterior pituitary differ from the posterior pituitary gland in the following: a) Site of hormone release? b) Production of hormones? c) Types of hormones produced?

-Releases Tropic Peptide hormones (hormones that control other glands) made via endocrine cells within itself into the hypophyseal system capillaries.

-Releases Peptide hormones (Oxytocin, Vasopressin) synthesized by neurons in the hypothalamus into the blood(not into the portal circulation)

What is the typical chain of events that releases hormones from the anterior pituitary gland?

1. Hypothalamic Activation: Stimuli act on the hypothalamus, triggering it to secrete a hypophysiotropic hormone.

2. Portal System Travel: This hormone travels down the hypothalamo-pituitary portal vessels directly to the anterior pituitary.

3. Anterior Pituitary Secretion: The portal hormone binds to specific endocrine cells, stimulating (or inhibiting) the release of an anterior pituitary hormone into the general circulation via hypophyseal system capillaries.

4. Target Gland Action: The anterior pituitary hormone travels through the body to activate a third endocrine gland, which secretes its final hormone to cause a cellular response.

What are six hormones released by anterior pituitary? Responses of each hormone?

• Growth Hormone (GH): Stimulates the liver to secrete IGF-1 (insulin-like growth factor-1) and directly targets organs to promote protein synthesis, bone growth, and metabolism.

• Thyroid-Stimulating Hormone (TSH): Targets the thyroid gland to stimulate the synthesis and release of thyroid hormones

• Adrenocorticotropic Hormone (ACTH): Targets the adrenal cortex to stimulate the secretion of glucocorticoids (primarily cortisol).

• Prolactin (PRL): Targets the breasts/mammary glands to stimulate breast development and milk production (lactation).

• Luteinizing Hormone (LH): Targets the gonads; triggers ovulation and progesterone production in ovaries, and stimulates testosterone production in testes.

• Follicle-Stimulating Hormone (FSH): Targets the gonads; stimulates egg/follicle development in ovaries and sperm production in testes.

Describe the hormones released by the thyroid gland

The thyroid gland synthesizes and secretes three primary hormones that play a vital role in regulating the body's metabolism, growth, and development:

• Thyroxine/Tetraiodothyronine T4: The primary hormone produced by the thyroid gland. It regulates metabolic rate, heart function, and body temperature.

• Triiodothyronine T3:It binds to cellular receptors to strongly influence metabolic processes, oxygen consumption, and energy generation.

• Calcitonin: Produced by the parafollicular cells (C-cells) of the thyroid, this hormone helps regulate blood calcium levels.

What is the typical chain of events that releases hormones from the thyroid gland?

• Secretion of the thyrotropin-releasing hormone (TRH).

• Elevating concentration of TRH stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH).

• TSH stimulates the thyroid gland to secrete T3 and T4 producing a negative feedback action on the anterior pituitary and hypothalamus.

• Thyroid hormones arrive at target cells.

What are the three main actions that thyroid hormones affect the body? What are

T3 and T4?

• T3 (Triiodothyronine)/T4 (Thyroxine)

• Regulating Basal Metabolic Rate (BMR): They control how fast the body burns calories and consumes oxygen to produce energy. This directly influences weight gain or loss and determines how effectively your body processes carbohydrates, lipids, and proteins.

• Maintaining Thermoregulation (Body Temperature): Thyroid hormones stimulate heat production by activating specific cellular processes.

• Supporting Growth and Development: Working alongside growth hormones, they are absolutely critical for proper bone growth, muscle development, and brain maturation (especially during childhood and fetal development).

Describe the hormones released by the adrenal cortex

• Glucocorticoids (primarily Cortisol): These hormones help the body manage stress, suppress inflammation, increase blood glucose levels, and regulate metabolism.

• Mineralocorticoids: regulate the body's salt, water, and electrolyte balance

• Androgens: Weak sex hormones produced in both males and females that contribute to secondary sex characteristics, important as precursors for estrogen and testosterone in other tissues.

What is the typical chain of events that releases hormones from the thyroid gland?

• Hypothalamus: When the body detects a need for increased metabolic rate (such as during cold exposure or stress), the hypothalamus releases Thyrotropin-Releasing Hormone (TRH).

• Anterior Pituitary: TRH stimulates the anterior pituitary gland to synthesize and secrete Thyroid-Stimulating Hormone (TSH) (also known as thyrotropin) into the bloodstream.

• Thyroid Gland: TSH binds to receptors on the follicular cells of the thyroid gland, stimulating them to produce and release thyroid hormones—primarily Thyroxine (T4​) and a smaller amount of Triiodothyronine (T3).

• Negative Feedback: Circulating levels of T3 and T4​ feed back to inhibit the production and release of both TRH from the hypothalamus and TSH from the pituitary, maintaining metabolic homeostasis.

What is the role of cortisol?

Cortisol is a vital glucocorticoid that maintains internal homeostasis. During a stress response, its roles change dramatically:

• maintains the responsiveness of target cells to epinephrine and norepinephrine 

• “check” on the immune system 

• mediates gluconeogenesis, lipolysis, and inhibition of insulin actions, all of which liberate energy sources (glucose, fatty acids) required to cope with stress. 

• Inhibits “nonessential” processes ex. reproduction, immune function.

• differentiation of fetal tissues

Describe the hormones released by the pancreas

• Insulin: Released in response to high blood sugar (fed state).

• Glucagon: Released in response to low blood sugar (fasting state).

What is the blood sugar set point? What happens when blood sugar spikes/drops?

-70 to 120 mg/dL during the day, and under 90–100 mg/dL while fasting

-The pancreas releases insulin. Causing GLUT4 transporters to move to cell membranes, drawing glucose out of the blood into the cell and storing it as glycogen (in liver/muscles) or fat.

-When Blood Sugar Drops: The pancreas releases glucagon. Glucagon targets the liver to break down stored glycogen back into glucose (glycogenolysis) and create new glucose (gluconeogenesis), raising blood sugar back up.

Which cells detect the change, and what responses occur to high and low blood sugar?

• High Blood Sugar Correction:

  • Detected by: Beta cells Act as the main glucose sensors. They have a special transporter called GLUT1 that allows glucose to enter the cell freely.

  • Response: Secretion of insulin,Glucose Uptake in Muscles and Fat. Liver Storage (Glycogenesis):

• Low Blood Sugar Correction:

  • Detected by: Alpha cells in the pancreatic Islets of Langerhans.

  • Response: Induce the liver to produce glucose via glycogenolysis and gluconeogenesis. The hypothalamus induces the adrenal medulla to secrete epinephrine and norepinephrine.

At rest, how much (percentage) of blood is directed to the muscles? Kidneys? Brain? How much is in the heart?

• Brain 650ml (13%)

• Heart 215ml (4%)

• Skeletal muscle 1030ml (20%)

• Skin 430ml (9%)

• Kidneys 950ml (20%)

• Abdominal organs 1200ml (24%)

• Other 525ml (10%)

What is the difference between hydrostatic pressure and resistance? What happens to resistance as a tube increases in length?

The outward push exerted by moving blood against the walls of a blood vessel.

The friction blood encounters as it flows through blood vessel

Resistance increases linearly with the length of the tube.

What is (blood) viscosity? How does viscosity affect resistance? How does the

radius of a tube affect resistance?

Blood viscosity is a measure of the internal friction or "thickness" of blood.

Resistance increases linearly as blood viscosity increases.

A tiny change in radius causes a massive change in resistance.

Based on Poiseuille’s Law, which has a higher resistance: vein, venule or capillary?

Capillary because it has the smallest radius.

Describe the electrical events that lead to heart contraction.

-A coordinated conduction pathway that spreads impulses from the top chambers to the bottom chambers, triggering cellular calcium release and muscle shortening

The sinoatrial node is described as a pacemaker… what does that mean?

Spontaneously generates the electrical impulses that set the rhythm and pace for the entire heartbeat

Describe how depolarization is moved through the heart. How does this precise movement of electrical activity affect heart contraction?

Known as the cardiac conduction system, ensures that the heart chambers contract in a specific order to pump blood efficiently

1.Sinoatrial (SA) Node Initiation.

2.Atrial Depolarization.

3.Atrioventricular (AV) Node Delay.

4.AV Bundle (Bundle of His).

5.Bundle Branches.

6.Purkinje Fibers.

7.Ventricular muscle cells

• Pacemaker potential initiates an action potenti

The action potential is initiated by the nodal cells. How is this achieved?

They have an unstable membrane potential baseline called a pacemaker potential that continuously drifts upward until it fires.

What are the two types of calcium channels that influence action potential?

• T-type Calcium Channels (Transient): These open briefly during the pacemaker potential (the slow drift phase). They allow a quick influx of Ca²⁺ to help push the cell membrane from its resting baseline up to its firing threshold.

• L-type Calcium Channels (Long-lasting): These snap open precisely at threshold (-40mV). They stay open longer, allowing a massive influx of Ca²⁺ that creates the actual depolarization spike of the action potential.

Describe the major events of the nodal cell action potential.

The Pacemaker Potential (The Slow Upward Drift)-The membrane potential spontaneously drifts upward from -60 mV to a threshold of -40 mV.

The Depolarization Phase (The Rapid Spike)-T-type and L-type voltage-gated calcium channels begin to open Massive influx of Ca shoot in the charge -40 mV to a positive peak of around +10 to +20 mV.

The Repolarization Phase (The Reset)-The Ca channels close and K channels open= outflux of K+ leads back to its baseline of -60 mV.

Describe the major events of the cardiac muscle action potential

• Phase 0 (Depolarization): Fast Na⁺ channels snap open. Massive Na⁺ influx causes a rapid electrical spike from -90mV to +20mV.

• Phase 1 (Initial Repolarization): Na⁺ channels close; a brief outflux of K⁺ causes a tiny downward dip in voltage.

• Phase 2 (The Plateau): L-type Ca²⁺ channels open (Ca²⁺ flows in) balancing out K⁺ flowing out. This prolongs contraction so the heart can empty.

• Phase 3 (Rapid Repolarization): Ca²⁺ channels close; K⁺ channels fully open. K⁺ rushes out, resetting the cell back to -90mV.

• Phase 4 (Resting Potential): Cell sits stable at -90mV via Na⁺/K⁺ pumps until the next heartbeat signal arrives.

What is an ECG? What does it measure?

Detection of the spread of cardiac cell depolarization and repolarization from the surface of the body.

What are the specific waves and events that are shown on a ‘normal’ ECG wave? How long is the normal ECG?

• P Wave- Atrial depolarization leading to atrial contraction.

  • Normal duration/size: About 0.06 to 0.12 seconds.

• PR Interval-The time from the start of the P wave to the start of the QRS complex. Atrial to Ventricular conduction

  • Normal duration: 0.12 to 0.20 seconds.

• PR Segment- Flat line between P wave and QRS. AV node delay

• QRS Complex- Ventricular depolarization, triggering ventricular contraction.

  • Normal duration: 0.06 to 0.10 seconds.

• ST Segment- Flat line from end of S to start of T. Early ventricular repolarization

• T Wave- Ventricular repolarization (the electrical recovery and relaxation of the lower chambers).

  • Normal duration: About 0.10 to 0.25 seconds.

• Q-T Interval- The total time taken for both ventricular depolarization and repolarization.

  • Normal duration: Varies with heart rate, typically roughly 0.35 to 0.44 seconds.

• R-R Interval-Times between R waves. Used to calculate Heart Rate

What is a lead? What does a lead measure? Where are the 3 standard leads placed?

An ECG Lead is a specific electrical view of the heart's electrical activity. It measures the voltage difference between a negative and a positive electrode.

Right Arm (RA), Left Arm (LA), and Left Leg (LL).

What events occur during systole? Diastole? How does it affect pressure in the aorta? Blood volumes in chambers?

Systole is the period of cardiac muscle contraction and blood ejection.

Diastole is the period of cardiac muscle relaxation and blood filling.

Together, they dictate the pressures in the aorta and the volume of blood remaining in the heart chambers.

What roles do the valves serve during contraction? What is a heart murmur?

They ensure the strictly one-way flow of blood and prevent dangerous backward leakage.

Murmur indicates turbulent blood flow due to narrowed or leaky valves; holes in the interventricular septum

What is cardiac output?

The total volume of blood pumped by the heart—specifically by one ventricle—per minute

Cardiac Output=Heart Rate x Stroke Volume (amount of blood ejected per heartbeat)

How does the sympathetic innervation affect cardiac output? Parasympathetic?

-(The "Fight or Flight" Response)

Dramatically increases cardiac output by acting on both the heart rate and the force of contraction.

-(The "Rest and Digest" Response)

Decreases cardiac output primarily by slowing the heart down.

Describe variables that affect cardiac output

Cardiac Output=Heart Rate x Stroke Volume (amount of blood ejected per heartbeat)

Describe how blood flows through the vascular system.

Flows in a continuous, one-way loop driven by pressure gradients created by the heart.

What is normal blood pressure? What is Mean Arterial Pressure?

-Systolic pressure equal or less than 120 mmHg AND a diastolic pressure equal or less than 80 mmHg

-(MAP) is the average blood pressure flowing through a patient’s arteries during a single complete cardiac cycle.

Understand how the sphygmomanometer works? Why do you need to listen for

systolic pressure first?

-A sphygmomanometer (blood pressure cuff) works by temporarily stopping blood flow through an artery and then slowly releasing the pressure to listen for the sounds of blood rushing back in.

-Because you are listening for the exact point where blood flow transitions from being completely blocked to tapping its way through the artery.

Where are the major baroreceptors located?

High-pressure stretch receptors two in the carotid sinuses and the aortic arch 

• Also located in systemic veins, pulmonary blood vessels, and walls of the heart

Amine hormones such as dopamine are amino acid derivatives. Other examples are:

• Thyroid hormones

• Catecholamines (such as epinephrine): secreted by the adrenal medulla and the hypothalamus

Receptors

 Bind to hormones and exert an action 

• Steroids and thyroid hormones: inside target cells

• Peptide hormones and catecholamines: on the plasma membrane

What is Stress and how is it related to Cortisol.

Stress: disruption of homeostasis; increased cortisol is a critical response 

Cardiac cycle length? Systole and diastole length?

For a typical heart rate of 72 beats/minute, each cardiac cycle lasts approximately 0.8 seconds, with 0.3 seconds in systole and 0.5 seconds in diastole.