Circulation [part 1]

TRANSPORT IN ANIMALS [part 1]

A) General characteristics of a circulatory system

B) The development of blood systems in animals

C) Composition of blood

D) The circulatory system

E) Formation of tissue fluid

F) The heart

G) Functions of mammalian blood

H) Oxygen dissociation curves – The Bohr shift






F) The heart



Function of a circulatory system:

To provide rapid mass flow of materials:

Blood flow

Vein

from one part of the body

to another over distances where

diffusion would be too slow

On reaching their destination, materials must be able to:

pass through the walls of the circulatory system into the organs or tissues

Three distinct characteristics of every blood system:

1. a circulatory fluid, the blood

2. a contractile pumping devise [either a modified blood vessel or a heart]

3. tubes through which the fluid can circulate, the blood vessels

Two distinct types of blood systems in animals:

Open circulation Closed circulation

blood does not stay

in the blood vesselsblood stays in the

blood vessels

most arthropods

Open circulation in Closed circulation in

echinoderms

most cephalopod

molluscs (octopus)

annelids

vertebratessome molluscs

Distribution of blood to the tissues is :

poorly controlled

Open circulation Closed circulation

well controlled

Blood and tissue fluid in:

mix

Open circulation

Closed circulation

remain separate

In an open circulation:1. The heart pumps blood into

an aorta: branches into

arteries.

2. These arteries open into a

series of blood spaces

collectively called the

haemocoel.

3. Blood under low pressure

moves slowly between the

tissues, gradually percolating

back into the heart through

open-ended veins.

In a closed circulation blood is:

pumped by the heart rapidly around the body under high pressure and back to the heart

Characteristics of:Open circulation Closed circulation1. Blood flow is slow and at a low pressure due to the absence of smooth muscles.

1. The speed of circulation is more rapid due to the presence of muscular and contractile blood vessels.

2. Direct exchange of materials between the cells and the blood because of the direct contact between them.

2. The supply and removal of materials to and from the tissues by the blood is enhanced, thereby increasing the efficiency of circulation.

3. The respiratory pigment, when present, is dissolved in the plasma of the blood and there are no red corpuscles

3. The volume of blood flowing through a tissue or organ is regulated by the contraction and relaxation of the muscles of the blood vessels.

Advantages of a closed circulation:

1. Blood can flow more rapidly through vessels

than through intercellular spaces, so:

rapid transport of nutrients and wastes

to and from tissues more rapidly.

A closed circulation:

can support higher levels of metabolic activity than open systems, especially

in larger animals

Insects do not depend on their circulation for O2 to reach the cells, but have the tracheal

system.

How can highly active insect species achieve high levels of metabolic output with their open

circulatory system?

Advantages of a closed circulation:2. By changing resistances in the blood vessels, blood

can be directed to specific tissues

e.g. during

exercise blood

is:

diverted to:

active

muscles

away from:

the gut

Advantages of a closed circulation:

3.

can be kept

within the

vessels

Cellular elements

Large molecules that

aid in the transport of

hormones

Nutrients






F) The heart



Annelids (fig. 2)

are coelomate animals

separates the body

wall from the internal

organs

independence of movement of internal structures such as the gut

a blood system has evolved which connects gut and body wall

However, a connecting system between the two

regions is needed

The earthworm:has a well-developed blood system

blood circulates in blood vessels

2 main blood vessels: run the length of the

body: one dorsal one ventral

are connected by blood vessels in each segment

1. Near the front of the animal:

5 pairs of connecting vessels are contractile and act as pumps

How is blood moved forwards in an earthworm?

5 hearts

2. The main blood vessels can also pump blood.

contains haemoglobin dissolved in the plasma rather than in red blood cells

Blood in an earthworm:

Arthropods (fig. 3a) : have an open blood system

the coelom is drastically reduced

and its place taken by the haemocoel

What is the ‘haemocoel’?

Crayfish

Haemocoel

The haemocoel is a network of blood-filled spaces called sinuses in which the

internal organs are suspended.

Crayfish

Haemocoel

Sinus

Arthropod blood is:

colourless contains no haemoglobin

The insect’s heart is a flexible tube and runs:1. longitudinally

through the thorax

& abdomen Heart

2. along the inside of the dorsal

body wall

A small valve-like opening through which blood enters

the heart

The dorsal vessel is:

Dorsal vessel is called

HEART in the abdomen

closed at the

posterior end

open at the

anterior end

The heart is divided

into chambers

separated by ostia Heart

13 chambers in

cockroach

Does not possess :

- valves

- musculature

Is a simple tube

Each chamber has a pair of:alary muscles

expand & contract to facilitate the flow of haemolymph through the heart

Position of heart in vertebrates:

ventral position near the front of the animal

Vertebrates:

arteries carry blood away from the heart

veins carry blood back to the heart

O2 is carried by

haemoglobin in red blood cells



C) Composition of bloodD) The circulatory system


F) The heart



Blood is:a liquid tissue made up of several types

of cell which are bathed in plasma

Whole Blood Sample

Sample Placed in Centrifuge

Blood Sample That Has Been

Centrifuged

Plasma

PlateletsWhite blood cells

Red blood cells

Platelets

White blood cells

Red blood cells

plasma

Percentage by volume of:

What is ‘serum’?

plasma without fibrinogen

Plasma is:

a pale straw-coloured liquid

made up of: 90% water 10% substances

Constituents of PLASMA Major FunctionsWater Solvent for carrying other

substancesSalts

SodiumPotassiumCalciumMagnesiumChlorideHydrogen carbonate

Osmotic balance,pH buffering, Regulation of membrane permeability

Plasma ProteinsAlbuminFibrinogenAntibodies

Osmotic balance,pH buffering,Clotting,Immunity

Substances transported by bloodNutrients (e.g. glucose, vitamins)Waste products of metabolismRespiratory gasesHormones

CELLULAR ELEMENTS 45%

CELL TYPE NUMBER(per mm3 of blood)

FUNCTIONS

Erythrocytes(red blood cells)

5–6 million

Transport ofoxygen (and carbon dioxide)

Leucocytes(white blood cells) 5,000–10,000

Defence andimmunity

Basophil

Eosinophil

Neutrophil

Lymphocyte

Monocyte

Platelets

250,000–400,000 Blood clotting

Where are blood cells formed?

Pluripotent stem cells in the red marrow of bones

Platelets

Pluripotent: capable of giving rise to

several different cell types

PlateletsRed blood cells

White blood cells

B cells T cells

Lymphoidstem cells

Pluripotent stem cells(in bone marrow)

Myeloidstem cells

Erythrocytes

Platelets Monocytes

Neutrophils

Eosinophils

Basophils

Lymphocytes

What is ?A hormone made by:

Kidneys

Released when:

Oxygen levels are low

Causes:

RBC formation

Negative Feedback

Control

RED BLOOD CELLS

ERYTHROCYTES

RBCsmall biconcave discs

surface area efficiency for diffusion of

O2 & CO2

lack a nucleus when mature

very thin cells: efficient diffusion of gases across surface

RBC are flexible & elastic:

to squeeze through narrow capillaries

Cardiac muscle and capillary

Erythrocytes in single file – capillary is so narrow

RBC make up about half the volume of blood

i.e. blood has an enormous oxygen-carrying capacity

Erythrocytes(45% of total blood)

Plasma(55% of total blood)

Leucocytes & Platelets(< 1% of total blood)

haemoglobin: the oxygen-carrying protein pigment combines reversibly with O2

RBC: packed with haemoglobin

Haem

Haemoglobin

Hb + O2 :

- in areas of high O2 concentration

Hb releases the O2 :

- in regions of low O2 concentration

Oxyhaemoglobin

LOADING

UNLOADING

RBC lack mitochondria. Give two advantages of this.

1. more room for carrying haemoglobin

2. respire anaerobically : do not use up any of the O2 they carry

RBC contain the enzyme:

plays a role in CO2 transport

carbonic anhydrase

Life span of RBC

about 3 months

then destroyed in: liver or spleen

What happens to haemoglobin when an old RBC is broken down?

Protein portion:

amino acids

Iron in haem:

stored in liver as ferritin (an iron-

containing protein)

Remainder of the haem molecule:

broken down into two bile pigments

(bilirubin and biliverdin)

White blood cellshave a nucleus

larger than RBC

present in smaller amounts

life span is normally a few days

A blood smear

All WBC are capable of a:

crawling movement called amoeboid movement

Lecuocytes can be divided:

Granulocytes Agranulocytes

Lymphocyte

Neutrophil

Basophil

Eosinophil

Monocyte

Lobed nucleus

Oval or bean-shaped nucleus

72% of total WBC count 28%

Neutrophils:70% of WBCs

Function Phagocytise & destroy

bacteria

Lobed

nucleus

First cells to respond to infection

Eosinophils:

1.5% of WBCs but numbers increase with allergic conditions

Function:

Secrete antihistamine

Eosin-staining granules

Basophils:

0.5% of all white blood cells

granules stain blue with basic dyes such as methylene blue

Function:

produce: heparin (anti-clotting protein) histamine (involved in inflammation)

Monocytes:spend 30-40 hours in

the blood then enter the tissues where they become macrophages

macrophages:

are phagocytic

Lymphocytes: produced in:

thymus gland lymphoid tissues

from cells which originate in the bone

marrow

Lymphocytes:

are rounded have a small quantity of cytoplasm

Considering the shape of the lymphocyte, do you expect amoeboid movement to be extensive or limited?

Limited

are found in:

Lymphocytes:blood

lymph

body tissues

two types occur: T cells B cells

life span varies from: a matter of days to many years

involved in immune reactions

Fig. 22.12Stem cell

B cell

T cell

B cell

T cell

Red bone marrow

Circulation

Pre-B cell

Pre-T cell

Circulation

Pre-T cell

Thymus Lymphnode

Circulation

Platelets:

irregularly shapedmembrane-bound cell

fragmentusually lacking nuclei

life span: 5-9 days before

destruction in liver & spleen

Platelets are formed from:special cells (megakaryocytes) in the

bone marrow

Function of Platelets:start the clotting process

Break in Capillary

Wall

Clumping of Platelets Clot forms

Fibrin fibres

Practical work to include the microscopic examination of stained

blood films and the identification of cells.

LymphocyteNeutrophils

Platelets Erythrocytes Monocyte




D) The circulatory systemE) Formation of tissue fluid

F) The heart



Three features of human circulation:

1. It is a double circulation. pressure is restored &

boosted before the blood is circulated to the rest of the body

Pulmonary circulation:

through lungs

SystemicCirculation:

through the rest of the body

Pulmonary vein

Aorta

Hepatic artery

Renal arteryRenal vein

Hepatic portal vein

Vena cava

Pulmonary artery

2. The organs are arranged in parallel rather than in series. loss in pressure, oxygen and nutrients at each

stage – if in series

Pulmonary vein

Aorta

Hepatic artery

Renal arteryRenal vein

Hepatic portal vein

Vena cava

Pulmonary artery

3. A portal vessel links the gut to the liver. the liver monitors blood passing

through it to help keep a constant composition

Double circulation of blood in humans

blood passes through the heart twice for each circuit of the body

Single circulation

Double circulation

FISH

BIRDS & MAMMALS have true double

circulations

the beginnings of a double circulation are seen in amphibians

reptiles have an almost completely divided heart

Why is a single circulation less efficient than a double circulation?

Drop in pressure as blood passes through the gills

Three layers in an artery & a vein

1. Tunica intima [endothelium]

an inner lining of squamous epithelium

2. Tunica media a middle layer of

smooth muscle + elastic fibres

3. Tunica externa an external layer

consisting mainly of inelastic collagen fibres)

Compare anatomy of:

Artery

VeinNote the much thinner walls in veins.

Artery and Vein

Two reasons for walls of arteries being thick and the middle layer being mainly composed of elastic

fibres.

1. To dilate but not rupture when the heart forces blood into them at high pressure

2. Between beats the arteries undergo elastic recoil and contract, tending to smooth out the flow of blood along their length

Muscles in blood vessels regulate the distribution of blood to an organ:

Normal arteriole

Vasoconstriction

Resistance = Decreased flow

Resistance =

Vasodilation

Caused by:

CO2

Cold

CO2

HeatIncreased flow

Veinsact as blood reservoirsstore: 65% - 70% of the body’s total

blood volume

Veins contain one-way valves

Varicose Veins:Damaged valves

in veins

When body muscles contract, they exert

pressure and squeeze the veins

flat, helping the blood to return to the heart.

How does blood return to the heart?

Capillaries• are very small - about the

diameter of a red blood cell

• capillary walls are: a single layer of very thin

endothelial cells, attached at their edges

and surrounded by a basement membrane

Endothelial cells

Question: Section C [MAY, 2010]

Use your knowledge of biology to describe the selective advantage of the following adaptations.

The diameters of red blood cells and the blood capillaries in which they flow are approximately the same. (5 marks)

Basement membrane

Blood moves slowly in capillaries as the diameter of RBC is approximately the same as that of capillaries. This gives time for:

oxygen to be released from RBC and to diffuse into the tissue fluid.

another function of RBC is to carry carbon dioxide away from tissues in the form of carbamino-haemoglobin. Ample time is available for carbon dioxide to enter the RBC.

Flow of blood into capillaries can be controlled by:

sphincters present in many arterioles at the point where they

enter the capillaries

Sphincters are circular muscle fibres:

When contracted: prevent blood flow into the capillary network

Pressure is reduced in smaller vessels because:

Arterioles are highly branched.Capillaries contribute an enormous

surface area.

Fig. 16 Blood pressure throughout the human circulatory system.

Blood flows slowly through capillaries. Why?

Due to a very large cross-sectional area[velocity is inversely proportional to cross-

sectional area

Capillary beds are:

permeable to:

water, ions, small molecules

impermeable to:

large proteins

Blood cells, most proteins.

Vesicles; large, lipid-insoluble (proteins)Filtration; fluid and

small, lipid-insoluble molecules (water, amino acids,NaCl, glucose,urea)

Diffusion; lipid-soluble molecules(O2, CO2, lipids)

Label the veins, venules, arteries, arterioles, and capillaries

Across which vessels do materials diffuse (cross into and out of the blood)?

Indicate where the heart is

veinvenules

artery

arteriolescapillaries

Artery Vein CapillaryTransports blood away from the heart.

Transports blood towards the heart.

Link arteries to veins

Tunica media thick and composed of elastic and smooth muscle tissue.

Tunica media relatively thin and only slightly muscular. Few elastic fibres.

No tunica media. Only tissue present is squamous endothelium. No elastic fibres.

Artery Vein CapillaryNo semilunar valves (except where leave heart).

Semilunar valves at intervals along the length to prevent backflow of blood.

No semilunar valves.

Pressure of blood is high and has a pulse.

Pressure of blood low and no pulse detectable.

Pressure of blood falling and no pulse detectable.

Artery Vein CapillaryBlood flow rapid. Blood flow slow. Blood flow

slowing.Low blood volume. Much higher blood

volume than capillaries or arteries.

High blood volume.

Blood oxygenated except in pulmonary artery.

Blood deoxygenated except in pulmonary vein.

Mixed: oxygenated & deoxygenated blood.





E) Formation of tissue fluidF) The heart



Tissue fluid: forms by filtration when blood passes through

capillaries is a watery liquid that resembles plasma minus its

proteins

Tissue cell

Capillary

Tissue fluid forms Tissue fluid

returns

Direction of blood flow

Arterial end of capillary

Venous end of capillary

15 µm

What forces are involved in tissue fluid formation?

two opposing forces :

Blood pressure forces water and small solutes out

Osmotic pressure

created by the large molecules that cannot leave (also called colloidal osmotic pressure)

Arterial end Venous end

Formation & drainage of tissue fluid

What can you say about the collodial osmotic pressure value?

is relatively constant along the capillary

Blood, tissue fluid & lymph

10%

90%

Kwashiorkor (protein deficiency) results in the swelling (oedema) of the belly

an osmotic effect

the ability of the blood to take up water from the body cavity by osmosis is reduced because of the deficiency of blood proteins (solutes)

An extensive system of blind-ending tubes which carries lymph

What is the Lymphatic System?

Lymph is:a clear, watery, sometimes faintly

yellowish fluid derived from tissue fluid

similar in composition to blood plasma

1. does not contain erythrocytes

2. contains a much lower concentration of protein

The Lymphatic System consists of: Lymphatic

vessels Lymphoid tissues

and organs

[Lymphoid tissue: where

lymphocytes develop e.g.

lymph nodes]

Lymph nodes occur all over the body

600-700 lymph nodes

Lymph contains white blood cells

Lymphocytes in lymph node

http://www.med-ars.it/lymphnodes/lymph%20node.jpg

Three functions of the lymphatic system:

1. Removes excess tissue fluid from tissues

2. Absorbs and transports fats from the digestive system

Blood capillary

Thin epithelium

Lacteal (lymphatic

vessel)

3. Plays a role in immunity.

A lymph node filters microbes.

How does lymph return to the blood? Via the:

right

lymphatic duct

left thoracic duct

http://www.rahulgladwin.com/medimages/plog-content/images/free-usmle-medical-images/thorax-images/thoracic-right-lymphatic-duct.jpg

Both the circulatory & the lymphatic system possess:

Unidirectional or

bidirectional flow of lymph?

How is lymph moved through lymph vessels?

By contraction of the muscles surrounding

them

By semi-lunar valves present in the major vessels

How is backflow prevented?

What happens if the lymphatic vessels become blocked as by parasitic worms?

A nematode worm infects the lymph nodes and

blocks the flow of lymph throughout the body.

Elephantiasis Disease or Filariasis:

transmitted by a mosquito bite

[over 130 million people are

infected]

Wuchereria bancrofti

Female worms: 8 -10 cm long Males: 4 cm

This question is concerned with the lymphatic system.

a. What is lymph? (2)

Lymph, a colorless to yellowish fluid whose composition is similar to that of blood except that it does not contain red blood cells or platelets, and contains considerably less protein.

Question: [SEP, 2009]

b. What are the main functions of the lymphatic system? (2)

- collects fats from the ileum via lacteals

- plays a role in immunity. Fluid is filtered in lymph nodes which contain lymphocytes that kill microbes

- drains tissue fluid and returns it to the bloodstream.

c. Briefly describe how fluid enters and leaves the lymphatic system. (3)

Tissue fluid enters the lymphatic system located at the venous end of a capillary. Lymph is drained into the subclavian vein by the right or thoracic lymph ducts.

d. Compare the composition of lymph with that of blood plasma in the following two situations:

i) Lymph that has just left a lymph node; (1)

Lymph is richer in lymphocytes than plasma as it leaves the lymph nodes.

ii) Lymph formed in the vicinity of the small intestine.

Is rich in fats as lacteals absorb triglycerides. (1)

e. How is lymph propelled through the lymphatic system? (2)

By contractions of skeletal muscles. Valves inside the lymphatic vessels prevent backflow.

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Circulation [part 1]