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HUMAN BODY: SEXUAL DIMORPHISM, COELOM SEXUAL DIMORPHISM Sexual dimorphism is well marked in humans. (i)

Generally males are taller than female.

(ii)

Beard, moustaches and hair on the chest are absent in females.

(iii)

Larynx is more apparent in males.

(iv)

Skin is more hairy and coarse in males.

(v)

Breasts are well developed in females.

(vi)

Shoulders are broader in males.

(vii) Hips are broader in females. (viii) Male has copulatory organ (penis). Female has clitoris (vestigial penis). (ix)

A pair of scrotal sacs containing tests are present in males.

(x)

Males have low pitched voice, however, females have high pitched voice.

TERMS INDICATING DIRECTIONS Some of the terms indicating directions are given in the following table :

BODY WALL The body wall consists of skin, muscle layer and parietal peritoneum. (i) Skin. It is the external covering of the body. It bears hair except in certain regions. It is attached to the underlying muscle layer by areolar tissue. (ii) Muscular layer. It consists of striped muscle fibers. These muscles are attached to the skeleton. (iii) Parietal Peritoneum. It is a thin membrane made up of tessellated epithelium (modified squamous epithelium which is composed of flattened cells with wavy outlines). Parietal peritoneum forms outer layer of the coelom and secretes coelomic fluid to keep the internal organs moist.

COELOM Coelom is a space which is externally lined by parietal peritoneum and internally by visceral peritoneum. These two membranes develop from the mesoderm of the embryo. Human coelom is divisible into four compartments.

(i)

(ii)

(iii)

Coelom in Human Body Paricardial cavity. The heart is surrounded by two membranes (outer parietal pericardium and inner visceral pericardium). Between these two membranes is the pericardial cavity filled with pericardial fluid. Pleural cavities. Each lung is surrounded by two membranes (outer parietal pleura and inner visceral pleura). Mediastinum. The mediastinum is the median septum (partition) between the two lungs and, therefore, includes the mediastinal pleurae of both the sides, but it is generally defined as the interval between the two pleural sacs. It contains trachea, oesophagus, thoracic duct, thymus, heart, lymph nodes, muscles, arteries, veins, nerves. Both the pericardial cavity and pleural cavities are present in the thorax; therefore, they are the parts of the thoracic cavity. Abdominal cavity. It lies in the abdomen. It is lined by a thin parietal peritoneum. The visceral peritoneum surround the organs of the abdominal cavity. The thoracic and abdominal cavities are separated by a dome-shaped membranous muscular structure called diaphragm. The lower portion of the abdominal cavity is called pelvic cavity. The viscera of abdominal cavity include the stomach, small intestine, most of large intestine, liver, spleen, pancreas and kidneys. The pelvic cavity is roughly funnel shaped. The viscera of the pelvic cavity are the internal reproductive organs, the inferior portion of the large intestine and the urinary bladder. The human body cavities can be arranged into two groups – dorsal (posterior) cavities and ventral (anterior cavities) cavities.

Body cavities of Human Body Dorsal (posterior) cavities. They include the cranial cavity, containing the brain and the spinal cavity, containing the spinal cord. The spinal and cranial cavities are continuous with one another. 2. Ventral (anterior) cavities. They include the orbital cavities containing the eyes, the nasal cavities of the nose, buccal cavity or mouth, thoracic or chest cavity, abdominal cavity and pelvic cavity. The abdominal and pelvic cavities are continuous with one another and are sometimes called together as the abdominopelvic cavity. Mesentery. A double layer of peritoneum that suspends organs in the abdominopelvic cavity is called mesentery. The mesentery which suspends the stomach, intestine, colon, rectum, ovary, oviduct and uterus from the body wall is termed as mesogaster, mesentery proper, mesocolon, mesorectum, mesovarium, mesosalpinx and mesometrium respectively. Omentum. A double layer of mesentery between certain abdominal organs is called omentum. The lesser omentum lies between the liver and stomach and the greater omentum lies between the stomach and small intestine. 1.