bio 1002 Circulation and gas exchange

Circulatory systems –why have them?

Circulatory systems link exchange surfaces with cells throughout the body

They link exchange surfaces with cells throughout the body

Gases (oxygen, carbon dioxide)

Nutrients

Hormones

Three types of exchange

Three types of exchange systems (ish)

Gastrovascular cavity (not a system)

Open circulatory system

Closed circulatory system

Gas and nutrient exchange in a gastrovascular cavity: Simple form

Diffusion of gasses and nutrients between environment and cells of the body

Mouth opens into a cavity made of radial canals leading to and from a circular canals.

Cilia circulate fluid through the canals

Gas and nutrient exchange in a gastrovascular cavity Complex form

Diffusion of gasses and nutrients between environment and cells of the body

Mouth and pharynx open into a highly branched cavity

why The need for a circulatory system

Larger body size

More complex body plans

Higher metabolic rates

Circulatory systems evolved along with specialized tissues for digestion, and more complex cell-to-cell communication via hormones

Circulatory systems have vessels and a pumping mechanism (organism specific)

Open circulatory system

Fluid is called hemolymph

The heart pumps hemolymph into sinuses (spaces surrounding organs)

Chemical exchanges (gases, nutrients) happens in the sinuses

Relaxation of the heart draws hemolymph back into heart

hemolymph

fluid of an open circulatory system

Closed circulatory system

Fluid is called blood

Blood is contained within vessels and heart (never leaves the system)

Chemical exchanges (gases, nutrients) happens between the blood and interstitial flued and between interstitial fluid and body cells

Blood travels through branched system of blood vessels in one direction

Arteries

carry blood away from the heart

 Central cavity lined with endothelium (single layer of flattened epithelial cells

 Smooth muscle and connective tissue to aid in support and contraction

 Connective tissue is much thicker and stronger, giving arteries elastic walls

 No valves

endothelium

skin type cells

(single layer of flattened epithelial cells

Arterioles

branches of the artery within organs

Capillaries

microscopic blood vessels

Venules

branches of the veins within organs

Veins

carry blood back to the heart

Central cavity lined with endothelium (single layer of flattened epithelial cells

 Smooth muscle and connective tissue to aid in support and contraction

 Wall is about 1/3 size of an artery

 Valves to maintain unidirectional blood flow at low pressure

The heart chambers

Atrium/atria

Ventricle(s)

4 types of vertebrate circulatory systems

 Single circulation (e.g., fish)

 Double circulation

systemic circuit

pulmonary circuit

systemic circuit

 One circuit between heart and the rest of the body (systemic circuit)

pulmonary circuit

 One circuit between the heart and the gas exchange surface

 Three types of double circulation

 Pulmocutaneous circuit

 Pulmonary circuit – incomplete septum

 Pulmonary circuit – complete septum

Single circulation

One circuit from heart to gas exchange surface (gill capillaries), body and back to heart

Heart has a single atrium and single ventricle

Single circulation Disadvantages?

-blockages effect everywhere

-not efficient

-heart is a muscle but only gets oxygen poor blood

Double circulation pulmocutaneous circuit/amphibian circulation

One circuit from heart to gas exchange surface (lung and skin capillaries)

One circuit from heart to rest of body

Heart has two separate atria and a ridge in the ventricle to partially separate oxygen rich/oxygen poor blood

Double circulation pulmonary circuit/reptilian circulation

One circuit from heart to gas exchange surface (lung capillaries)

One circuit from heart to rest of body

Heart has two separate atria and an incomplete septum in the ventricle to partially separate oxygen-rich/oxygen poor blood

Double circulation pulmonary circuit/mammal and bird circulation

One circuit from heart to gas exchange surface (lung capillaries)

One circuit from heart to rest of body

Heart has two separate atria and two separate ventricles (4 chambers)

Muscle walls of the ventricles are much __ than the atria

thicker

__ between the atria and ventricles (atrioventricular valves) and between ventricles and blood vessels (semilunar valves) prevent backflow

Valves

atrioventricular valves

Valves between the atria and ventricles

semilunar valves

valves between ventricles and blood vessels

lub dub sound

The blood recoiling against the AV valves makes a “lub” sound Vibration caused by the closing of the semilunar values makes a “dup” sound

Heart murmur

when blood squirts backwards through a defective valve

Can be born with, or as a result of infection

Does not always impact blood flow efficiency

Can be corrected surgically

the two circuits (pulmonary and systemic) happen , not __ as shown in the diagram!

simultaneously , in sequence

Heart contractions (cardiac cycle)

1. atrial and ventricular diastole

• Both A and V are relaxed; blood flows from body into atria and then ventricles

2. atrial systole and ventricular diastole

• A contraction forces all blood into ventricles

3. ventricular systole and atrial diastole

• A relaxed, V contracts to pump blood into the large arteries (pulmonary artery and aorta

Cardiac output

Amount of blood pumped by each ventricle per minute

Heart rate

rate of contraction (number of beats per minute)

Stroke volume

amount of blood pumped by a ventricle in a single contraction

ECG (or EKG) electrocardiogram

measures electrical impulses produced by the SA node and the AV node

: sinoatrial node (aka pacemaker) atrioventricular node

why does blood flow slower in capillaries

Surface area of capillaries is MUCH bigger than arteries and veins

How many capillaries in a human body?

b.7 billion

blood pressure movement

Pressure drops from heart through to veins

Blood moves 500 times slower in the capillaries than aorta (0.1 cm/sec vs 48 cm/s; this allows exchange of materials between blood and interstitial fluid

Measuring blood pressure

The cuff is inflated until the pressure closes the artery

The pressure on the gauge exceed that in the artery

The cuff deflates gradually. As it reaches a pressure just below the pressure in the artery, the sounds of blood flowing can be heard in the stethoscope.

The pressure in the gauge is the systolic pressure

The cuff deflates until the blood flows freely and the sounds disappear..

The pressure in the gauge is the diastolic pressure.

What percentage of your capillaries have blood flowing through them right now?

a. 5-10%

movement through capillaries

Capillaries have no smooth muscle so blood flow is regulated with either

Smooth muscle contraction in the arteriole

Precapillary sphincters

Movement of fluids between capillaries and surrounding tissues is via

Endocytosis and exocytosis of the endothelium

Diffusion

Via pores

Movement of fluid out of the capillaries is via blood pressure

Movement of fluid into the capillaries is via blood proteins

You body has about _ L of blood

5

Human blood is made up of two components:

Plasma (55%) Cellular elements (45%)

Blood plasma

Plasma is 90% water

Serum

plasma from which the clotting factors have been removed

Cellular elements of blood

Erythrocytes (red blood cells) are the most numerous

There are 25 trillion erythrocytes in your body

There are 5 types of leukocytes (white blood cells)

Platelets are pinched-off cytoplasmic fragments of bone marrow cells

Erythrocytes

red blood cell

Lack nuclei

Lack mitochondria

Small biconcave disks

Lack of nucleus means more room for hemoglobin proteins

Hemoglobin is an iron containing protein that transports O2

Leucocytes

5 types

• neutrophils

• basophils

• eosinophils

• monocytes

• lymphocytes

Their main function is to fight infections.

They travel outside the circulatory system and can be found in interstitial fluid and the lymphatic system

Platelets

• Pinched off cytoplasm of specialized bone marrow cells

• 2-3 μm

• Aid in blood clotting

What happens when cut – blood cell level

1. Damaged blood vessel endothelium exposes connective tissue in the vessel wall to blood. Platelets in the blood attach to collagen fibres in the connective tissue. This makes nearby platelets sticky

2. Platelets form a plug to prevent blood loss

3. In larger breaks, the plug is reinforced by fibrin threads

gas exchange vs respiration

gas exchange:

• Uptake of molecular O2 from the environment and discharge of CO2 to the environment

• Happens in nostrils/tracheal lungs (human) Happens in gills (fish

respiration:

• Cellular process referring to the energy transformation of sugars to ATP

• Happens in the mitochondria (all organisms)

Important concept – partial pressure

Partial pressure: the pressure exerted by a gas or mixture of gasses.

Gasses always diffuse from regions of higher partial pressure to regions of lower partial pressure.

Gas exchange in water

When in equilibrium, the partial pressure of gasses in air equal that in water

However, concentrations differ because gases are less soluble in water than in air

More difficult to extract oxygen from water than air

Cells that carry out gas exchange have a __ that must be in contact with a solution; therefore all respiratory surfaces are always __

plasma membrane , moist

Gas exchange always takes place via __

diffusion

Diffusion is __when the area for diffusion is large and the path is short, because __

fastest

 This influences morphology of respiratory surfaces  They tend to be large and thin

Gills

Out-foldings of the surface of the body suspended in water

Movement of the gills in water (ventilation) maintains the partial pressure gradients necessary for gas exchange

Different strategies for this…

Tracheal systems

Lungs

Lungs are infoldings of the body

The gas exchange surface of the lung is not in direct contact with the rest of the body; thus the circulatory system bridges this gap and moves gases to/from the lungs/rest of body

airway pathway

Air enters via nostrils; nose hairs filter out particles, sample odors, and warm and humidify the air

The larynx contains muscular bands called vocal cords. Air passing these makes sounds

Air travels down the trachea (windpipe) \

Trachea separates into two bronchi (one to each lung)

Each bronchus branches into finer and minor tubes called bronchioles

The epithelium of the “tree” is covered mucus which traps particulates and cilia which beat these back upward to the pharynx, where it can be swallowed

At the end of each bronchiole are air sacs called __

alveoli

Humans have __ alveoli

millions

What is the total surface of the alveoli?

Positive pressure breathing

Bellows-breathing

• Efficient because air passes over the gas exchange surface in only one direction

• Incoming fresh air does not mix with air that has already carried out gas exchange

Negative-pressure breathing

Pulling air in, rather than pushing it into the lungs

Muscle contraction actively expands the thoracic cavity; this lowers the pressure in the lungs to below that of the outside world

Gas flows from high to low pressure, so can travel down the breathing tubes to alveoli

Tidal volume

how much air you inhale/exhale

What is human tidal volume at rest?

c. 500 mL

Vital capacity

tidal volume during maximal inhalation and exhalation

 What is your max vital capacity if female?

 What is your max vital capacity if male?

Residual volume

: air that remains in lungs after a forced exhalation

Why do we not exhale all the air in our lungs?

Mixing fresh air with oxygen depleted air means the maximum PO in the alveoli is always less than the atmosphere

Homeostatic control of breathing

Putting the circulatory and gas exchange systems together

As breathing increases, circulation does too, so that exchange of O2 and CO2 between blood and lungs is maintained

Movement of gases between alveoli and blood vessels is influenced by partial pressures

Pigments in the blood (respiratory pigments) facilitate this

respiratory pigments

Pigments are proteins that circulate with blood and bind to specific cells

E.g., Hemoglobin binds to erythrocytes (red blood cells)

Each iron atom can bind 4 molecules of O2

4 iron atoms per hemoglobin molecule

Adaptations for gas exchange

include pigments that bind and transport gases

Birds can breathe at high altitudes because they inhale fresh air each breath

High altitude animals often have elevated hemoglobin

Diving mammals slow their metabolism and store oxygen in blood rather than lungs (via myoglobin)