The Heart Beat

Pages 222-224

stethoscope

Cardiac Cycle

• The heart pumps in a cycle of filling, contracting and relaxing

• Systole: when the cardiac muscle contracts

• Diastole: when the cardiac muscle relaxes

• Makes the sound Lub-Dup

• 1 complete cycle takes about 0.80 - 0.85 seconds

1 Cardiac Cycle

Time Atria Ventricles

0.15 sec (atrial systole)

Systole Diastole

0.30 sec(ventricle systole)

Diastole Systole

0.40 sec Diastole Diastole

When the atria contract, the ventricles are relaxed and filling with blood.

When the ventricles contract, the AV valves close, preventing blood from flowing back into the atria.

After the ventricles contract, the cardiac muscle relaxes.

Lub-Dup

• Lub: vibration caused by the atrioventricular valves closing (ventricle closing)

• Dup: vibration caused by the semilunar valves closing

1 Cardiac Cycle

Time Atria Ventricles

0.15 sec(atrial systole)

Systole Diastole

0.30 sec(ventricle systole)

Diastole Systole (LUB)

0.40 sec Diastole Diastole (DUP)

When the atria contract, the ventricles are relaxed and filling with blood.

When the ventricles contract, the AV valves close (LUB), preventing blood from flowing back into the atria.

After the ventricles contract, the cardiac muscle relaxes (DUp).

Heart Mur-mur

• A slight slush sound after the “lub”– Ineffective valves:

allows blood to pass back into the atria after the AV valve closed

What controls the heartbeats?

• Intrinsic Control (internal)– Uses nodal tissue which possess muscular

and nervous characteristics– Beats independent of

outside nervous stimulation

• Sinoatrial (SA) node• Atrioventricular (AV) node

Sinoatrial (SA) node “Pacemaker”

• Located in the upper dorsal (back) wall of the R. atrium

• Initiates heart beats• Sends out excitation

impulses every 0.85 sec• Result: Atria contract• When it fails, heart still

works via AV node, butslower

Atrioventricular (AV) Valves

• The impulse from the SA node will reach the AV node

• Sends message to contractthe ventricles via AV bundle andpurkinje fibers

What controls the heartbeats?

• Extrinsic Control (external)– Heart rate control center = Medulla Oblongata

in the brain

• Uses the Autonomic System to alter heart beat

Sympathetic Parasympathetic

(not under conscious control)

Sympathetic Division

• Increases heart rate (heart rate > 100 beats/min)

• Increases activity or stress– “fight or flight” response

• Increases nodes’ activity when we are active or excited

What increases heart rate?

• Hormones like adrenalin / epinephrine

• Increased body temperature

• Exercise

• Drugs (caffeine, nicotine)

Parasympathetic System

• Decreases heart rate

• Promotes functions at resting state, normal activities– “rest and digest”

response

The Electrocardiogram

• Listen the heart beat (audio)

The Electrocardiogram (ECG)

• A recording of the electrical changes that occur in 1 cardiac cycle

• SA node starts

the cycle

The Electrocardiogram (ECG)

• P wave (0.15s)– occurs

just before atrial systole

• QRS complex (0.3s)– Occurs just before

ventricle systole

• T wave (0.4s)– When the ventricles

recover from contraction

The Electrocardiogram (ECG)

• ECG can be used to detect any abnormalities of the heart (irregular heart beats)– Example: Heart mur-mur

• Play audio of heart murmur

Blood&

Blood Pressure

Sphygmomanometer

How is blood pressure (BP) measured?

• Measured on the brachial artery in the upper arm

• Expressed in millimeters of mercury (mmHg)

• BP reading consists of 2 numbers– Systolic and diastolic pressures respectively– Example: 120/80

Ventricles contractBlood into arteries

Ventricles relax bw heart beats

• Systolic pressure– Blood being forced into the arteries during

ventricular systole

• Diastolic pressure– The pressure in the arteries during ventricular

diastole

Blood Pressure (BP)

• Pressure is created by the force with which the left ventricle contracts – blood leaves and enters the aorta then into

the systemic arteries under pressure– in general, as blood

moves away from the heart, its pressure decreases

High and Low BP

• Hypotension (Low blood pressure)– Reduces your capacity to transport blood– Causes: dehydration, heart failure,

anaphylaxis (life-threatening allergic reaction)

• Hypertension (High Blood pressure)– Can weaken an artery and eventually lead to

the rupturing of the vessel– BP 140/90– Causes: smoking, drugs, increase stress, diet

Blood

Pages 226 - 231

Blood

• Is a connective tissue (like bone and cartilage) because cells work together to provide critical links of – Supply– Defense– Communication

Function of Blood

• Transport – (nutrients, wastes, hormones)

• Regulatory – (body temp, BP, pH ~7.4)

• Protective – (against invasion of pathogens, blood loss)

4 Components

• To accomplish the functions, blood requires 4 components:

1. Plasma (55%)

2. Red blood cells (RBCs 45%)

3. White blood cells (WBCs)

4. Platelets (<1%)Formed elements

plasma

red blood cell

white blood cell

platelets

Plasma

• A straw-coloured liquid• Contains

– Water (90-92%)– Plasma Proteins (7-8%)– Salts (<1%)– Gases– Nutrients– Nitrogenous wastes– Hormones, vitamins

RBCs (Erthrocytes)

• Life span: 4 months• Made in bone marrow of the

– Skull, ribs, vertebrae and ends of long bones

• Mature RBCs lack nucleus• Shape: biconcave disk

– Increases flexibility for moving through capillaries

– Increases surface area for gas diffusion

• ~ 4-6million RBCs per mm3 of bloodText: figure 12.12Capillary + RBC

Why are RBCs Red?

• RBCs are red because they contain hemoglobin (Hb)

Hemoglobin (Figure 12.12)

• Respiratory pigment, red in colour

• Each molecule has 4 polypeptide chains– Each chain has a heme, a complex iron group– Picks up oxygen from lungs – Release oxygen in tissues– Carries carbon dioxide from tissues back to

lungs

RBC Degradation

• RBCs are destroyed in the liver and spleen

• iron in hemoglobin (Hb) is recycled

• Heme is excreted as bile

RBC Reproduction

• Happens in the bone marrow

Stem cell(with nucleus)

- Divide (mitosis)& Shrinks- Take up Hb(can be re-used from old destroyed RBCs)

Nucleusdisappears

Discharge RBCs

into bloodIf O2 levels decrease:

- RBC reproduction

- a result of hemorrhaging, blood transfusion, high altitude

Anemia

• A deficiency in hemoglobin (the iron) or RBCs

• Less oxygen delivered to tissues results in lack of energy

• Always feel tired• Kidney produces erythropoietin (hormone)

to speed up maturation of RBCs in bone marrow

WBCs (Leukocytes)

• Many different types• Larger than RBC• Has nucleus• Lack hemoglobin• Produced in bone marrow• 700RBC : 1WBC• 4,000-11,000 WBCs per mm3

• Fight infections• Develops immunity of body• Resist pathogens

WBCs (Leukocytes)

• We identify different types of WBCs based on:– Shape, size of nucleus, cytoplasm granules

(granular vs agranular)

Focus on 2 Types of WBCs

• Phagocytes (Macrophages)– Engulf and destroy invaders,

dead cells

• Lymphocytes (T-cells & B-cells)– Create antibodies

produce immunity to disease

Antibodies and Antigens

• Antigens – any molecule, usually a protein or carb, that stimulates the immune system

• Antibody – prevents antigens from binding onto cells

Comparing RBCs and WBCS

RBCs WBCs

Both develop from identical

stem cells in bone marrow

Look identical Different types

Mature, has no nucleus Mature, has nucleus

Smaller Bigger

Carry O2/CO2 Fights diseases

Platelets (Thrombocytes)

• Make 200 billion/day

• No nucleus

• Very tiny in size

• Irregular in shape

• Made from nucleated cells in bone marrow

• Essential for blood clotting (coagulation)

Blood Clotting (Figure 12.14)

Damaged tissue

Platelets gather at wound to seal leak

Tissue and platelets release prothrombin activator(converts plasma protein prothrombin to thrombin)

Fibrinogen activated

Ca2+

Fibrin forms – forms a net around Platelet and plug the leak

Capillary Exchange (in the systemic circuit)

Capillary Exchange (in the systemic circuit)

• Exchange of fluid is control by 2 forces– Osmotic pressure (OP)

• Created by salts and plasma proteins• Causes water to move from tissue fluid (fluid bw the

tissue cells) to the blood

– Blood pressure (BP)• Causes water to move from blood to tissue fluid• At the atrial end: BP is higher, OP is lower

– Water leaves from blood

• At the venous end: BP is lower, OP is high– Water enters into blood

• Midway of capillary: no net movement bc the 2 forces cancel each other out – DIFFUSION takes over

Midway of Capillary(for the systemic circuit)

• DIFFUSION takes over because OP and BP cancels each other out:– Nutrients and O2 diffuse out of capillary (for

absorption into tissue)– Wastes (CO2) diffuse into capillary (for

transport to the lungs)

Movement is reversed in the pulmonary circuit.

Excess Tissue Fluid

• Collected by lymphatic capillaries

• Tissue fluid contained in lymphatic vessels are called lymph

Returned to the systemic venous blood when the vessels enter subclavian vein (shoulder region)

Lymphatic System

• Closely associated with the Circulatory System

• 3 functions– Lymphatic capillaries take up excess tissue

fluid and return it to the blood– Small lymphatic capillaries absorb fats from

the digestive tracts (lacteals in villi)– Helps defend body against pathogens

Lymph Capillaries & Nodes

• Lymph capillaries– Take up excess tissue fluid from the

capillaries in the circulatory system

• Lymph nodes– Small, oviod– Cleanses lymph– Contains lots of – B and T cells