.png){kind=icon}
What is a hormone?
A hormone is a chemical messenger in the body.
Can you think why, in physiological terms, the testes lay outside the abdominal cavity?
The external location of the testes helps them to maintain a temperature 3–5oC lower than the core body temperature, which is necessary for optimum sperm production.
What are the differences (if any) between a gamete, a zygote and an embryo?
Gametes are the haploid germ cells in the gonads. A male and female gamete will fuse to form a diploid zygote, which, after several mitotic cell divisions, becomes an embryo.
Why do you think microtubules are sometimes referred to as the ‘cytoskeleton’?
Microtubules provide a supporting framework for the cell.
Can you describe three similarities and three differences between mitosis and meiosis?
Similarities: both are forms of cell division, both involve spindle fibre formation and both involve DNA replication.
Differences: meiosis occurs only in the gonads, occurs only in diploid cells and involves chromosomal crossover; mitosis occurs all over the body, occurs in diploid or haploid cells, and does not involve chromosomal crossover.
The sperm’s tail is sometimes described as a ‘flagellum’. What are the differences and similarities between flagella and cilia?
Similarities: motility and internal structure.
Differences: flagella are longer and fewer in number (per cell).
What is meant by the term ‘blood-testis barrier’?
A physical barrier between the circulatory system and the lumen of the seminiferous tubules in the testes, formed by tight junctions between adjacent Sertoli cells.
What are the constituents of semen?
Semen is a mixture of sperm and various fluids secreted by the male accessory sex glands. The fluid is rich in fructose, enzymes, citric acid, acid phosphatase and lipids.
Explain why the formation of polar bodies is a physiological necessity.
Polar bodies result from asymmetrical cell division during oogenesis. In order to conserve nutrients, the daughter cells destined to become the ovum acquire nearly all the cytoplasm of the parent cell. The remaining daughter cells, the polar bodies, contain very little cytoplasm and usually die.
Compare and contrast the structure and function of microvilli and cilia.
Microvilli: non-motile, do not contain microtubules, serve to increase cell surface area to enhance diffusion of substances across the cell membrane.
Cilia: usually motile, contain microtubules, serve to move liquid over the surface of an epithelium.
The word ‘pseudostratified’ is used in descriptions of columnar epithelium in various body sites. Can you explain what the word means?
‘Pseudo’ means false or apparent; ‘stratified’ means layered. So, ‘pseudostratified’ means false or apparent layering. Pseudostratified epithelium appears multilayered because the nuclei of adjacent columnar cells lie at different levels within the cell. However, as each cell remains in contact with the basement membrane, a pseudostratified epithelium consists of only one layer of cells.
Describe the difference between a diverticulum, a crypt and a gland.
The three structures can easily be confused. A gland is an organ with a secretory function. The secretions may enter the bloodstream directly (as in endocrine glands) or are expelled into a body cavity via ducts (as in exocrine glands). A diverticulum is a simple outpouching of a duct or channel, and a crypt is a deep invagination of an epithelium. Diverticulae and crypts may or may not have a secretory function.
How and why must the endometrium respond quickly to fluctuations in ovarian hormones?
The lining of the uterus is very sensitive to changes in circulating levels of ovarian hormones. The close proximity between the site of secretion and the target organ facilitates the rapid response. The fast response is required to prepare the uterus for implantation of a fertilized ovum.
Can you think of examples of metaplasia occurring elsewhere in the body?
Apart from the cervix, other sites of metaplasia include the respiratory tract (see Chapter 6), the lower oesophagus (see Chapter 8) and bladder.
Apart from the female external genitalia, where else might you find sebaceous glands?
Sebaceous glands may be found anywhere in the skin but are particularly abundant on the face and scalp (see Chapter 15).