Transport in Humans

Chapter Overview

8.1 The Circulatory System - Introduction & Anatomy

8.2 The Blood & Blood vessels

8.3 The Hear t & Cardiac Cycle 8.4 Heart Diseases

8.1.1 The need for transport

8.1.2 Double Circulation

8.2.1 Components of the Tissue Fluida) Blood Plasmab) Red Blood Cellsc) White Blood Cellsd) Platelets

8.2.2 Exchange of Substances and The Lymphatic System

8.2.3 Haemoglobin

8.2.4 Rejection and ABO Blood Group

8.2.5 Structure-function of blood vessels

8.4.1 Myocardial infarction

8.4.2 Causes of Heart Diseases

8.3.1. Structure and Function of heart

8.3.2 Heart valves, Systole and Diastole

Transport in Mammals

(a) Relate the structure of arteries, veins and capillaries to their functions.

(b) Describe the transfer of materials between capillaries and tissue fluid.

Objectives

Organisation of Blood Vessels

Arteries arterioles capillaries venules veins

TB PG 152

The Blood Vessels

There are 5 types of vessels in the mammalian circulatory system.

1. Arteries2. Arterioles3. Veins4. Venules5. Capillaries

TB PG 153

The Blood Vessels

Wavy elastic band

External layer(Loose connective tissue)

Middle layer (Smooth muscle & elastic fibres)

(Inner layer) Endothelium

Arteries

• Branches into smaller vessels called arterioles

• Transports oxygenated blood away from the heart

(except pulmonary artery)

Lumen

TB PG 153

The Blood Vessels

Veins

• Smaller vessels called venules come together to form vein

• Carry deoxygenated blood towards the heart

(except pulmonary vein)Bigger Lumen

External layer (loose connective tissue

Middle layer (Thinner smooth muscle and elastic fibre

Endothelium

TB PG 153

The Blood Vessels

Capillaries

• Smallest vessels of all

• Exchange of substances between blood and surrounding tissue (facilitated by one cell thick endothelium)

Lumen

One cell thick endothelium

TB PG 164

arteries capillaries veins• Carry blood away

from heart• Branches into

smaller vessels called arterioles

• Transports oxygenated blood away from the heart

(except pulmonary artery)

• connect arteries to veins

• Smallest vessels of all

• Exchange of substances between blood and surrounding tissue (facilitated by one cell thick endothelium.

• return blood to heart

• Smaller vessels

called venules come together to form vein

• Carry deoxygenated blood towards the heart

(except pulmonary vein)

Types of blood vessels

The Blood Vessels

Arteries Structure

• 3 layers of tissues

Endothelium (Tunica intima)

Smooth muscle & elastic fibres (Tunica media)

Loose connective tissue (Tunica externa)

TB PG 153

The Blood Vessels

Arteries Structure• Thick elastic, muscular walls Arteries receive blood directly from the heart at high pressure

To withstand high blood pressure, allowing them to receive blood from the heart.

Elasticity permits stretching and recoiling of the artery wall. This helps to push the blood along

• Smooth muscles contract or dilates lumen constrict or dilate thus

controlling blood flow

TB PG 153

The Blood Vessels

Arteries Structure

• Round cross-sectional lumen• Smaller lumen than veins

Due to presence of thicker layer of muscles

Constriction & dilation of an artery is brought about

by the contraction & relaxation of the muscles in

the arterial wall.

TB PG 153

The Blood Vessels

Veins Structure

• 3 layers of tissues

• Less elastic, muscular walls

• Presence of valves prevent backflow of blood

ARTERY VEIN

TB PG 154

The Blood Vessels

Veins Structure

• Larger lumen compared to artery

• Walls are less thick and muscular and contain less elastic tissue

Blood is under lower pressure, so walls need not be as strong

TB PG 154

The Blood Vessels

Veins Structure

• Presence of semi-lunar valves

Pressure in the veins is lower, so semi-lunar valves help prevent the backflow of blood

TB PG 154

MJR Biology Department

VeinSemi-lunar valve

1. Muscles contract, push against the walls of the blood vessels

2. Narrowing of vein causes blood cells to be pushed forward

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Varicose Vein

Varicose veins are distended branches of the major veins in the leg. They become distended due to failure of the valves in the main veins which allows blood to fall back down the leg (reflux)

Varicose Vein

Varicose veins are more common in women than in men, and are linked with heredity[6]. Other related factors are pregnancy, obesity, menopause, aging, prolonged standing, leg injury and abdominal straining. Varicose veins are bulging veins that are larger than spider veins, typically 3 mm or more in diameter

The Blood Vessels

Capillaries Structure• Walls are made up of only a single layer of flattened cells

called endothelium. Facilitate Rapid Exchange of substances between blood and surrounding tissue  Endothelium is selectively permeable – allows small substances to diffuse but not large substances.  Blood pressure in capillary is low thus there is more time for the exchange of substances.

TB PG 152

The Blood Vessels

Capillaries Structure

• Highly branched increase SA/V ratio compared to arteriole from which the branches originate.

Lower blood flow and blood pressure Allow for more time for exchange

TB PG 152

oxyhaemoglobincapillary

cell

Exchange of materials between the blood and the body cells

plasma

tissue fluid

O2 nutrientswater

white blood cells

Diffuse across the capillary wall

CO2waste products

Diffuse across the capillary

wall Squeeze through the wall

TB PG 164

Transport in Humans

Cell

CellCell

Cell

Cell

Cell

Cell

Cell Cell

Cell

Cell

Cell

CellCell

Cell

Cell

Cell

Cell

RBCRBC

ArterioleCapillaries

Venule

Exchange of substancesUseful materials such as glucose and oxygen are transported from plasma /RBC (higher concentration) to tissue fluid (lower concentration), down a concentration gradient, by diffusion. The useful materials in the tissue fluid will diffuse to the cells when concentration of these useful materials in the tissue fluid becomes higher than that in the cells. Osmosis will also occur.

Transport functionTB PG 164

Transport in Humans

Cell

CellCell

Cell

Cell

Cell

Cell

Cell Cell

Cell

Cell

Cell

CellCell

Cell

Cell

Cell

Cell

RBCRBC

ArterioleCapillaries

Venule

Exchange of substancesWaste products such as carbon dioxide and urea are transported from cells (higher concentration) to tissue fluid (lower concentration), down a concentration gradient, by diffusion. The waste products in the tissue fluid will diffuse to the plasma when concentration of the waste products in tissue fluid is higher than plasma.

Transport functionTB PG 164

Arteriole end

Venule end

Partially permeable

Allows small molecules to move through. Elastic molecules maybe able to squeeze through as well.

What is the structure of capillaries?

What does partially permeable mean?

What are the small or elastic molecules in blood?

- Plasma (water + small soluble molecules) - WBC

What are the big or less elastic molecules in blood?

- RBC - Plasma proteins

Formation of tissue fluid TB PG 164

Arteriole end

Venule end

Water, small soluble molecules and WBC

Water, small soluble molecules and WBC

High pressure at the arteriole end forces water, small soluble molecules and white blood cells out of capillaries through the partially permeable endothelium into the tissue fluid.

Red blood cells and big plasma proteins continue to move in the capillaries. As blood flows from the arteriole to venule end, the blood becomes concentrated with solutes, such as plasma proteins.

Water from tissue fluid moves into the blood by osmosis at the venule end and small soluble molecules move into the blood by diffusion.

Water, small soluble molecules

Water, small soluble molecules

Remaining tissue fluid is collected by lymphatic vessels. The fluid in lymphatic system is known as lymph. Lymph will be emptied to blood circulation through a vein near heart.

TB PG 164

Formation of tissue fluid

Blood pressure in different blood vessels

Comparing the Blood VesselsFeatures Arteries Veins Capillaries

Direction of blood flow

Away from Heart Towards Heart Arteriole Venules

Blood Oxygenated (except in pulmonary and umbilical arteries)

Deoxygenated(except in pulmonary and umbilical veins)

Oxygenated Deoxygenated

Blood Pressure Highest Lowest High LowBlood Flow Fast Slow Slow

Wall Structure Thick, elastic muscular Relatively thinner, less muscular

-One-cell thick endothelium

- Partially permeable.

- Branch repeatedly to increase surface area to volume ratio

Lumen Ø Smaller compared with vein of same Ø

Wider compared with artery of same Ø

Small enough only for 1 RBC to squeeze through

Valves Absent Present Absent

Comparing the Blood VesselsFeatures Arteries Veins Capillaries

Structure-Function relationship

-Thick muscular wall to withstand the high blood pressure of blood as it is forced out of heart

-Elasticity enables artery wall to stretch and recoil, causing bood flow in pulses (Spurts)

-- No semi-lumar valve

- Thinner muscular walls to withstand the low blood pressure.

-Less elastic tissue as blood flows more slowly

-Larger lumen to reduce resistance to slower blood flow

- Semi-lunar valves to prevent backflow of blood

-Thin layer of endothelium which is partially permeable to allow substance to diffuse quickly through the walls

- Branch into numerous branches for a larger surface area for exchange of substances between blood and tissue cells.

- Arterioles branch into capillaries to increase total cross-sectional area which lower the pressure and flow of blood slows down, giving more time for exchange of substances

Allows fluid to pass through

wall

Carries fluid at high pressure

Has least resistance to flow of fluid

A X Y ZB X Z YC Y Z XD Y X Z

The figure below shows three types of blood vessels (not drawn to scale) in the human body. Which of the following is true?

Lymphatic System

Movement of Blood Plasma into Body Tissues

• Blood in arterioles Higher pressure than capillaries

• Blood plasma hence forced to leave capillaries

• And enter body tissues

• Soluble proteins cannot pass through capillaries.

• Hence the fluid that enters the body tissues does not

contain these proteins.

• This fluid is known as interstitial fluid or tissue fluid.

Lymphatic System

Where does interstitial fluid goes?

• Collected in lymph vessels.

• Part of the lymphatic system.

Lymphatic System

Where does interstitial fluid goes?

• Returned back to bloodstream via left subclavian vein

Transport in Humans

Adapted from http://www.und.nodak.edu

ArteryVein