Structure of Human Heart

• The heart is a muscular organ covered by a double membrane called pericardium.
• The pericardial fluid of the pericardium lubricates the heart.
• The heart is divided into four chambers — two upper atria and two lower ventricles.
• The inter-atrial septum separates the two atria and the inter-ventricular septum separates the two ventricles.
• The atrium and the ventricle of each side are separated by the atrioventricular septum.
• Superior and inferior vena cavae open into the right atrium.
• The right ventricle opens into the pulmonary artery.
• Four pulmonary veins open into the left atrium.
• The left ventricle opens into the aorta.
• The opening between the right atrium and right ventricle is guarded by the tricuspid valve.
• The opening between the left atrium and left ventricle is guarded by the bicuspid (mitral) valve.
• The opening of the right ventricle into the pulmonary artery and the opening of the left ventricle into the aorta is guarded by the semilunar valves.

• Blood coagulation or clotting is the mechanism to prevent excessive loss of blood from the body.
• Reddish brown scum formed at the site of a cut is due to clot formed mainly of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped.
• Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin.
• Thrombins are formed from another inactive substance present in the plasma called prothrombin by an enzyme complex known as thrombokinase.
• Calcium ions play a very important role in clotting.

• Two blood groupings are done
• ABO and
• Rh

ABO grouping

• ABO grouping is based on the presence or absence of two surface antigen on the RBCs namely A and B.
• The plasma of different individuals contains two natural antibodies.
• The distribution of antigens and antibodies in the four groups of blood, A, B, AB and O.
• The blood of a donor has to be carefully matched with the blood of a recipient before any blood transfusion to avoid severe problems of clumping, which leads to destruction of RBC.
• Group ‘O’ blood can be donated to persons with any other blood group and hence ‘O’ group individuals are called ‘universal donors’.
• Persons with ‘AB’ group can accept blood from persons with AB as well as the other groups of blood, and such persons are called ‘universal recipients’.

Rh grouping

• The Rh antigen similar to one present in Rhesus monkeys is also observed on the surface of RBCs of majority of humans, hence the antigen is known as Rh antigen.
• The individuals having Rh antigen are called Rh positive (Rh+ve) and those in whom this antigen is absent are called Rh negative (Rh-ve).
• An Rh-ve person, if exposed to Rh+ve blood, will form specific antibodies against the Rh antigens, and hence Rh group should also be matched before transfusions.
• A special case of Rh incompatibility has been observed between the Rh-ve blood of a pregnant mother with Rh+ve blood of the foetus , which leads to a disease known as erythroblastosis foetalis.
• Rh antigens of the foetus do not get exposed to the Rh-ve blood of the mother in the first pregnancy as the two bloods are well separated by the placenta, during the delivery of the first child, maternal blood may get exposed to small amounts of the Rh+ve blood from the foetus and the mother starts preparing antibodies against Rh in her blood.
• In case of subsequent pregnancies, the Rh antibodies from the mother (Rh-ve) can leak into the blood of the foetus (Rh+ve) and destroy the foetal RBCs, which cause severe anaemia and jaundice to the baby leading to a condition known erythroblastosis foetalis.
• Erythroblastosis foetalis can be avoided by administering anti-Rh antibodies to the mother immediately after the delivery of the first child.

• Blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements.

There are many cellular structures in the composition of blood. When a sample of blood is spun in a centrifuge machine, they separate into the following constituents: Plasma, buffy coat and erythrocytes.

Plasma

The liquid state of blood can be contributed to plasma as it makes up  ~55% of blood. It is pale yellow in colour and when separated, it consists of salts, nutrients, water and enzymes. Blood plasma also contains important proteins and other components necessary for overall health. Hence, blood plasma transfusions are given to patients with liver failure and life-threatening injuries.

Red Blood Cells (RBC)

Red blood cells consist of Haemoglobin, a protein. They are produced by the bone marrow to primarily carry oxygen to the body and carbon dioxide away from it.

White Blood Cells (WBC)

White blood cells are responsible for fighting foreign pathogens (such as bacteria, viruses, fungi) that enter our body. They circulate throughout our body and originate from the bone marrow.

Platelets

Tiny disc-shaped cells that help regulate blood flow when any part of the body is damaged, thereby aiding in fast recovery through clotting of blood.

Spleen has a similar structure to a large lymph node, which primarily functions as a blood filter. The spleen plays an important role in the red blood cells also known as aserythrocytes and the digestive system. Old and damaged RBC’s are destroyed in the spleen and It is known as the RBCs Graveyard.

Function of spleen :

• The spleen is the largest organ of the lymphatic system. It keeps all the body fluids balanced.
• It is made up of a red pulp tissue that filters the old and damaged red blood cells.
• The important function of the spleen is to filter the blood. The spleen recycles the old and damaged red blood cells and the white blood cells are stored.
• Spleen also helps to fight against bacteria that cause diseases such as meningitis and pneumonia.

Based on the position of the ovary flowers are categorized to 3 types they are
: Hypogynous, Epigynous, and Perigynous flowers.
Hypogynous: Flowers in which the sepals, petals, and stamens are attached below the ovary are called hypogynous, and the ovaries of such flowers are said to be superior. 
Eg: tomato, tulip, and snapdragon.
Epigynous: Flowers in which the sepals, petals, and stamens appear to be attached to the upper part of the ovary due to the fusion of the hypanthium are called epigynous, and the ovaries of such flowers are said to be inferior.  Eg: daffodil
Perigynous: Flowers types in which the hypanthium forms a cuplike or tubular structure that partly surrounds the ovary are called perigynous. In such flowers, the sepals, petals, and stamens are attached to the rim of the hypanthium, and the ovaries of such flowers are superior.
 Eg: cherry, Prunus

• The mitochondria is a double-membraned cell organelle, known as the powerhouse of the cell which is present in all eukaryotic cells.
• It was first discovered by Albert von Kolliker in the year 1857.
• It was named as bioblast by Richard Altman in the year 1886.
• The term mitochondria was coined by Carl Benda in the year 1898. 

The discovery of mitochondria is accredited to the several scientists who contributed to the discovery of mitochondrion and identification of its structure and functions. The earliest accounts of description of mitochondria go back to 1840. However, Richard Altmann was the first one to recognize the occurrence of these organelles and called them bioblasts. The name mitochondria was coined by Carl Benda in 1898. Christian de Duve was a Belgian researcher who discovered lysosomes in 1949.

Macromolecules are basically polymers, long chains of molecular sub-units called monomers. Carbohydrates, proteins and nucleic acids are found as long polymers. Due to their polymeric nature and large size, they are known as macromolecules.

The large complex molecules having molecular weights more than one thousand Dalton which occur in colloidal state in the intercellular fluid are called macromolecules. They are formed by the polymerization of low molecular weight micromolecules. For example: Polysaccharides, proteins, lipids, etc.

Key is a taxonomical aid that helps in the identification of plant and animal species. These keys are based on similarities and dissimilarities in characters, generally in a pair called a couplet. Each statement in a taxonomic key is referred to as a lead. It is also useful in the identification of unknown organisms.

The full form of PPLO is Pleuron pneumonia-like organisms and the term used to describe the mycoplasmas. PPLO is the smallest cell or organism with the size of between 0.1 and 0.3 mm. Mycoplasma has included species discovered from pleural fluid of cattle suffering from pleuropneumonia.

The study of tissue is called as histology study of forms and shapes of any living thing is called morphology study of the internal cellular organs or parts of any living thing is called anatomy. Pathophysiology or physiopathology is a convergence of pathology with physiology.

• Tissues are organized in specific proportion and pattern to form an organ. Examples- stomach, lung, heart and kidney.
• When two or more organs perform a common function by their physical and/or chemical interaction, they together form organ system. Examples- digestive system, respiratory system, etc.
• Cells, tissues, organs and organ systems exhibit division of labor for the survival of the whole body.

The gram-positive bacteria retain the crystal violet colour and stains purple whereas the gram-negative bacteria lose crystal violet and stain red. Thus, the two types of bacteria are distinguished by gram staining.

The most abundant protein present in the animal world is collagen.

Collagen: - It is a protein made from amino acids, specifically glycine, proline, hydroxyproline, and arginine.

 In plants, the most abundant protein is Rubisco.

Glycolysis is the first stage of the breakdown of glucose in the cell. During glycolysis 2 ATP molecules are used up and four ATP molecules are generated. In the entire process of glycolysis, two NADH₂ molecules are also generated. When these molecules undergo ETS they will form 3 ATP per NADH₂  which means 6 ATP. Therefore the total ATP that are forming are 10 and as 2 ATP is used up the net gain will be 8.

In glycolysis, two molecules of ATP are consumed initially in converting glucose to fructose 1, 6-bisphosphate. Two triose phosphate molecules are formed from one glucose molecules. Four molecules of ATP are produced at substrate level phosphorylation. Therefore, net gain of ATP is 2ATP×2−2ATP=2.

Neurons or nerve cells can be up to 3 feet long. A typical neuron has a cell morphology called soma, hair-like structures called dendrites and an axon. Neurons are specialized in conveying knowledge throughout the body. The sensory neurons, motor neurons, and interneurons are three types of neurons. Neurons have a membrane built to forward information to other cells.

CELL THEORY

• Schleiden and Schwann together formulated the cell theory.
• Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells.
• Cell theory states that
• All living organisms are composed of cells and products of cells.
• All cells arise from pre-existing cells.

Flight adaptations found in birds
(i) Body is streamlined to reduce air resistance during flight.
(ii) Four limbs are modified into wings.
(iii) Wings have long quill feathers to increase the efficiency of heating of wings,
(iv) Pneumatic bones are present to reduce the body weight.
(v) High metabolic rate to provide energy.
(vi) Air sacs present in lungs help in double respiration.

Flight adaptations in birds
(i) Boat-shaped body helps to propel through the air easily.
(ii) Feathery covering of body to reduce the friction of air.
(iii) Holding the twigs automatically by hindlimbs.
(iv) Extremely powerful muscles that enables the wings to work during flight.
(v) Bones are light, hollow and provide more space for muscle attachment. Presence of pneumatic bones which reduce the weight of body and help in flight.

(vi) The first four thoracic vertebrae are fused to form a furculum for walking of the wings.

(vii) Lungs are solid and elastic and have associated air sacs.

(viii) The power of accommodation of eyes is well developed due to the presence of comb-like structure pecten. (ix) A single left ovary and oviduct to reduce the body weight.

REGULATION OF RESPIRATION

• A specialised centre present in the medulla region of the brain called respiratory rhythm centre is primarily responsible for this regulation.
• Another centre present in the pons region of the brain called pneumotaxic centre can moderate the functions of the respiratory rhythm centre.
• Neural signal from this centre can reduce the duration of inspiration and thereby alter the respiratory rate.
• A chemosensitive area is situated adjacent to the rhythm centre which is highly sensitive to CO₂ and hydrogen ions.
• Receptors associated with aortic arch and carotid artery also can recognise changes in CO₂ and H⁺ concentration and send necessary signals to the rhythm centre for remedial actions.

Blood transports CO₂ from the tissue cells to the lungs in three ways:

1. Dissolved in plasma : About 7 – 10% of CO₂ is transported in a dissolved form in the plasma.

2. Bound to haemoglobin : About 20 – 25% of dissolved CO is bound and carried in the RBCs as carbaminohaemoglobin (Hb CO₂ ) CO₂ + Hb → Hb CO₂ .

3. As bicarbonate ions in plasma about 70% of CO₂ is transported as bicarbonate ions. This is influenced by pC0₂ and the degree of haemoglobin oxygenation. RBCs contain a high concentration of the enzyme, carbonic anhydrase, whereas small amounts of carbonic anhydrase is present in the plasma.

→ At the tissues the pCO₂ is high due to catabolism and diffuses into the blood to form HCO₂ and H ions. When CO₂ diffuses into the RBCs, it combines with water forming carbonic acid (H₂ CO₂ ) catalyzed by carbonic anhydrase. Carbonic acid is unstable and dissociates into hydrogen and bicarbonate ions.

Carbonic anhydrase facilitates the reaction in both directions.

The HCO₃^- moves quickly from the RBCs into the plasma, where it is carried to the lungs. At the alveolar site where pCO₂ is low, the reaction is reversed leading to the formation of CO₂ and water. Thus CO₂ trapped as HCO₃^- at the tissue level is transported to the alveoli and released out as CO₂ . Every 100 mL of deoxygenated blood delivers 4 mL of CO₂ to the alveoli for elimination.

Transport of oxygen

• Haemoglobin is a red coloured iron containing pigment present in the RBCs.
• O₂ can bind with haemoglobin in a reversible manner to form oxyhaemoglobin.
• Binding of oxygen with haemoglobin is primarily related to partial pressure of O₂ and partial pressure of CO2, hydrogen ion concentration and temperature are the other factors which can interfere with this binding.
• A sigmoid curve is obtained when percentage saturation of haemoglobin with O₂ is plotted against the pO₂ and the curve is called the oxygen dissociation curve.
• pCO2, H⁺ concentration have effect on binding of O₂ with haemoglobin.
• In the alveoli, where there is high pO₂, low pCO₂, lesser H⁺ concentration and lower temperature, the factors are all favourable for the formation of oxyhaemoglobin, and where low pO₂, high pCO₂, high H⁺ concentration and higher temperature exist, the conditions are favourable for dissociation of oxygen from the oxyhaemoglobin.
• Every 100 ml of oxygenated blood can deliver around 5 ml of O₂ and each haemoglobin molecule can carry a maximum of four molecules of O₂.

1. The exchange of gases between air and blood takes place across the walls of the alveoli.
2. The human respiratory system:

• Tidal Volume (TV): Volume of air inspired or expired during a normal respiration, which is approx. 500 mL.
• Inspiratory Reserve Volume (IRV): Additional volume of air, a person can inspire by a forcible inspiration, which averages 2500 mL to 3000 mL.
• Expiratory Reserve Volume (ERV ): Additional volume of air, a person can expire by a forcible expiration, which averages 1000 mL to 1100 mL.
• Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration, which averages 1100 mL to 1200 mL.
• Inspiratory Capacity (IC): Total volume of air a person can inspire after a normal expiration, which includes tidal volume and inspiratory reserve volume ( TV+IRV).
• Expiratory Capacity (EC): Total volume of air a person can expire after a normal inspiration, which includes tidal volume and expiratory reserve volume (TV+ERV).
• Functional Residual Capacity (FRC): Volume of air that will remain in the lungs after a normal expiration, which includes ERV+RV.
• Vital Capacity (VC): The maximum volume of air a person can breathe in after a forced expiration, which includes ERV, TV and IRV.
• Total Lung Capacity: Total volume of air accommodated in the lungs at the end of a forced inspiration, which includes RV, ERV, TV and IRV.