physiology CA2 flashcards

Heart function as a synctium

What happens when one cardiac cell undergoes an action potential?

The impulse spreads via gap junctions, making all connected cells contract as one syncytium.

Some of the muscle fibres of heart are modified into a

specialized structure known as

pacemaker cells or P cells.

What forms the Pacemaker in the heart?

Sino atrial (SA) node

What is an Action Potential?

The change in electrical potential with the passage of an impulse along the membrane of a muscle or nerve cell.

How long is the refractory period in cardiac muscle compared to skeletal muscle?

Cardiac muscle: ~250 msec
Skeletal muscle: ~3 msec

What happens to the membrane during the refractory period?

It is refractory to further stimulation until contraction is over.

Why does the refractory period last longer than muscle contraction?

Prevents tetanus, ensuring normal heart function.

Why is a long refractory period important for the heart?

Prevents fatigue, allowing the heart to relax after each contraction.

How does the refractory period help with heart function?

Allows time for heart chambers to fill during diastole before the next contraction.

What are the Phases of Cardiac Potential

Phase 0: Depolarization
Phase 1: Repolarization
Phase 2: Plateau phase
Phade 3: Rapid Repolarization
Phase 4: Resting Phase

(Rapid Depolarization) What defines the first step of the action potential in cardiac muscle?

• Cause: Sodium (Na⁺) entry

• Duration: 3-5 milliseconds

• Ends with: Closure of voltage-regulated (fast) sodium channels

• Voltage change: Rises from -90 mV to +30 mV

What characterizes the plateau phase (step 2) of cardiac muscle action potential?

• Cause: Calcium (Ca²⁺) entry

• Duration: Approximately 175 milliseconds

• Ends with: Closure of slow calcium channels

• Significance: Prevents immediate muscle fiber relaxation

What occurs during the repolarization phase (step 3) of cardiac muscle?

• Cause: Potassium (K⁺) loss

• Duration: 75 milliseconds

• Ends with: Closure of slow potassium channels

• Result: Return of membrane potential towards resting state

Phase 4: Resting Potential What happens during this phase?

High Potassium (K⁺) Permeability

Conduction rate of atrial muscle

0.3 m/s

Conduction rate of atrial pathways

1 m/s

Conduction rate of AV node

0.05 m/s

Conduction rate of Bundle of His

1 m/s

Conduction rate of Purkinje system

4 m/s

Conduction rate of ventricular muscle

0.3 m/s

Where is the impulse velocity maximum?

Purkinje fibers

Where is the impulse velocity minimum?

AV node

Stroke volume (SV) is the volume of

blood pumped out of each ventricle per beat or contraction .

Stroke Volume depends upon

End diastolic Volume and Contractility (SV = EDV – ESV)

As the stroke volume increases what also increases?

cardiac output

Average heart rate

70 bpm

Average stroke volume

70−80 ml/beat

Average cardiac output

5000 ml/minute

Cardiac Output Calculation

Heart Rate x Stroke Volume

(the result is in ml or litre)

The stroke volumes for each ventricle are generally equal or unequal? what is the sv in a 70kg man

equal. 70ml.

End diastolic volume (EDV) is the ?.. Sometimes called the .. What increases with a increased EDV ?

volume of blood in the ventricles at the end of diastole.
called preload
Stroke volume increases

Total peripheral resistance is ?.. and what is it called ?..

Frictional resistance in the arteries.
called after load

Contractility is the

strength of ventricular contraction

Ejection fraction (EF)

– percentage of the EDV that is ejected per cardiac cycle.

CO = SV x HR

cardiac output = stroke volume x heart rate (ml/minute) (ml/beat) (beats/min)

Factors affecting the heart rate (HR)

Age, Autonomic Innervation, Hormones, Fitness Levels.

Factors affecting Stroke Volume (SR)

Heart Size, Gender, Preload.

Sympathetic nerve activity

affects the ventricular myocardium, increasing stroke volume

Parasympathetic nerve activity

affects the SA (sinoatrial) node, increasing heart rate.

What is the P-Wave on an ECG?

• Occurs when the Atria is full of blood

• SA node (Sinoatrial Node) fires electrical impulses

• Causes atrial depolarization

• Normal duration: 0.06 - 0.11 seconds

What is the QRS complex in an ECG?

• Indicates ventricular depolarization

• Triggers contraction of the ventricles

• Larger than the P wave due to greater tissue mass

What does the T-wave represent in an ECG?

What Does the T wave represent

ventricular repolarization immediately before ventricular relaxation

Larger P wave: It indicates

enlargement of atrium.

Enlarged R wave: It indicated

enlargement of ventricles.

Flatter T wave: It indicates

insufficient oxygen supply to myocardium.

Larger PQ interval: It indicates

formation of scar tissue in heart

Larger or Elevated ST segment: It indicates

acute myocardial infarction.

Resting coronary blood flow in human, average is approximately

225ml/minute. 0.7 to 0.8 ml per gram of heart muscle

what happens During diastole

cardiac muscle relaxes and no longer obstruct the blood flow through the left ventricular capillaries

During cardiac contraction what happens to the Intra myocardial layer of the heart muscle?

is much greater than the outer layer. compresses the sub endocardial blood vessels more than the outer vessel.

An individual’s blood pressure is affected by a number of factors. Name some

Age – It increases as you get older.

Gender – Men tend to have higher blood pressure than women.

Stress - Can cause increase blood pressure.

Diet – Salt and saturated fats can increase blood
pressure.

Exercise – Exercise lowers the blood pressure

Variations in Blood Pressure. Normal, Hypotension, Hypertension.

Human normal range is variable
Normal • 140–110 mmHg systolic • 80–75 mmHg diastolic

Hypotension • Low systolic (below 110 mm HG) • Often associated with illness

Hypertension • High systolic (above 140 mm HG) • Can be dangerous if it is chronic

Control of BP: Short term control

Mainly involves the baroreceptor reflex, chemoreceptor & circulating hormones

Control of BP: Long term control

Involves regulation of blood volume by the kidneys and Renin-angiotensin-Aldosterone System

The cardiovascular centre (CVC) is a collection of

interconnected neurons in the brain

The CVC receives, integrates & coordinates inputs from:

❖ Baroreceptors (pressure receptors)
❖ Chemoreceptor
❖ Higher centers in the brain

Baroreceptors are:

nerve endings sensitive to pressure changes. situated in the arch of the aorta

What triggers the RAAS cascade? and what does it lead to?

• Dehydration

• Na+ deficiency

• Hemorrhage

  
  leads to..
  

• Decreased blood volume

• Decreased blood pressure

• Kidney cells release renin

• Ultimately increases blood pressure and volume

DEFINITION OF SHOCK

tissues in the body don't receive enough oxygen and nutrients to allow the cells to function

Cardiogenic shock

occurs due to systolic or diastolic dysfunction

Hypovolemic shock

occurs due to intravascular fluid volume.

Obstructive shock

occurs when there is physical obstruction in blood flow

Distributive shock

is three (neurogenic, anaphylactic & septic)

Neurogenic shock

occurs from trauma that leads to spinal cord injuries.

Anaphylactic shock

acute life threatening hypersensitivity reaction to a sensitizing substance like drug, chemical, vaccine, food etc

Septic shock

Also known as blood poisoning. caused by infections that lead to bacteria entering blood.

Hypovolemic shock occurs when? and leads to what?

Decreased blood volume from:

• Accident

• Burn

• Diarrhea

• Vomiting

  
  and leads to
  Decreased venous return
  Decreased cardiac output
  Decreased tissue perfusion
  Decreased cellular metabolism

What triggers Neurogenic Shock?

Disruption of sympathetic nervous system

Vasodilation
Decreased bp
Decreased cardiac output
Decreased cellular oxygen supply
Decreased tissue perfusion
Impaired cellular metabolism

Anaphylactic shock

allergen , drug etc.

antigen antibody reaction
Vasodilation
Capillary permeability
Severe Broncho constriction
Decreased oxygen supply and utilization
Inadequate tissue perfusion

What characterizes the Gastric Phase?

• 60% of acid response

• Initiated by:

  • Gastric distention

  • Partial protein digestion

  • Gastrin release

What is the Cephalic Phase?

• Mediated by Vagus nerve

• 30% of meal response

• Starts with: Food smell Food taste Eating anticipation

Where are G cells Found? What do they Secrete?

gastric pits only in the Proximal gastric Area (PGA). secrete the hormone gastrin into the blood.

Where are Enterochromaffin-like (ECL) cells Dispersed among? what do they secrete

parietal and chief cells in the gastric glands of the oxyntic mucosa. secrete the histamine.

Where are D cells scattered in? What do they Secrete.

in glands near the pylorus but are more numerous in the duodenum, secrete the somatostatin.

What is AcetylCholine and where is it released from? What does it stimulate aswell?

neurotransmitter released from the intrinsic nerve plexuses. stimulates parietal and chief cells as well as the G cells and ECL cells

Gastrin are Secreted by _ in Response to..?

by G cells in response to protein products in the stomach lumen and in response to ACh.

Gastrin Stimulates ? promoting the Secretion of a ?

stimulates the parietal and chief cells, promoting secretion of a highly acidic gastric juice

Gastrin indirectly Promotes the secretion of?

HCl secretion by stimulating the ECL cells to release histamine.

Histamine is released from

ECL cells

Histamine acts locally on nearby parietal cells to

speed up HCl secretion and potentiates (makes stronger) the actions of ACh and gastrin.

Somatostatin

is released from the D cells in response to acid. It acts locally in negative-feedback fashion

Interstitial cells of Cajal network.

electrical pacemakers for smooth muscle cells

network with each other and are interposed between the smooth muscle layers, with synaptic like contacts to smooth muscle cells.

What are Secretin. and What is the stimulus for release

S cells of the duodenum. Presence of acidic chyme

What Cells are Cholecystokinin (CCK). and what Stimulates them for release

I cells of the duodenum and jejunum.

Presence of food in the duodenum

Intense peristaltic waves are observed during ..

observed during intestinal obstructions,

Function of Intense peristaltic waves

sweeps the contents of ileum into colon and relieves ileum of irritative chyme & excessive distension

Migrating Motor Complex function

sweeps the GIT tract having left over undigested food and prevents the backflow of bacteria from the colon into the ileum

The usual stimulus for intestinal peristalsis is

distention of the gut

if a large amount of food collects at any point in the gut

stretching of the gut wall stimulates the enteric nervous system

Functions of segmentation contraction

ensure completion of digestion.

Functions of segmentation contraction: Slow contractions permits

longer contact of the chyme with mucosal surface and permits absorption

CCK, Motilin, Gastrin, Ach, serotonin increases what?

increase the motility

Secretin and glucagon inhibits what?

inhibit the motility

what happens increasing Filtration Fraction

Increasing the filtration fraction also concentrates the plasma proteins and raises the glomerular colloid osmotic pressure

Proximal Tubule

A thick, constantly active segment of the nephron

Medullary Collecting Duct

final site for processing the urine

Glucose - Filtration, Reabsorption, Excretion, and Reabsorption Percentage
Back:

• Filtered: 180 g/day

• Reabsorbed: 180 g/day

• Excreted: 0 g/day

• Reabsorbed Percentage: 100%

Sodium - Filtration, Reabsorption, Excretion, and Reabsorption Percentage

• Filtered: 25,560 meq/day

• Reabsorbed: 25,410 meq/day

• Excreted: 150 meq/day

• Reabsorbed Percentage: 99.4%

: Water - Filtration, Reabsorption, Excretion, and Reabsorption Percentage

• Filtered: 169 L/day

• Reabsorbed: 167.5 L/day

• Excreted: 1.5 L/day

• Reabsorbed Percentage: 99.1%