Structure and Function of Mammary Gland

Female Breast

The mammary glands, sometimes known as the breasts, are auxiliary female reproductive glands that are involved in nursing after childbirth. Women's breast shapes change during the course of their lives. However, the breast's base has a rather stable size. Typically, it crosses the midclavicular line between the second and sixth ribs. It is located beneath the fascia that covers the pectoralis major in the subcutaneous tissue. The Cooper's ligaments, a group of muscle fibers in the connective tissue, support the breast.

Structures of Non-lactating Breast

There are roughly 20 (15-20) lobes in the breasts, which are secreting glands made primarily of glandular tissue. Alveoli and ducts make up the lobules that separate each lobe. Acini cells found in the alveoli make milk. Myoepithelial cells that surround the alveoli contract to push milk toward the nipples. Larger ducts are created when smaller lactiferous ducts, which transport milk from the alveoli, combine. Milk is collected by a number of large ducts called lactiferous tubules from one or more lobes that connect to the surface of the nipple.

Lactiferous tubules are not necessary. Myoepithelial cells are positioned longitudinally along the ducts, and when oxytocin is present, these smooth muscle cells contract, shortening and widening the tubule. During periods of active milk flow, the tubule may provide a momentary reserve for milk (while the myoepithelial cells are maintained in a state of contraction by circulating oxytocin).

The nipple, which is made up of erectile tissue, has an epithelium covering and contains simple muscle fibers that act like sphincters to control the flow of milk. The areola, a region of pigmented skin surrounding the nipple, houses Montgomery glands. These generate a substance resembling sebum that serves as lubricant during pregnancy and lactation.

Blood Supply of the Breast

The internal and external mammary arteries, as well as branches from the intercostal arteries, supply the breast with arterial blood. Around the nipple, the veins are arranged in a circle. Between two breasts, as well as into lymph nodes in the axillae and midiastinum, the lymph flows freely. An essential pathway for the quick spread of cancerous cells throughout the body is provided by the extensive lymphatic drainage of the breasts.

Nerve Supply of the Breast

The breast is supplied by the fourth, fifth, and sixth intercostal nerves.

Physiology of Lactation

Lactation is the term used to describe the production and ejection of milk. Colostrum is often secreted by the breast during pregnancy. However, excessive estrogen and progesterone production suppresses the pituitary. After placenta delivery, estrogen and progesterone levels decline, which prompts the anterior pituitary gland to secrete prolactin hormone, which starts the lactation process. The three stages of lactation's physiology are as follows:

• Initiation of milk secretion or lactogenesis: Oestrogen and progesterone levels fall after placenta birth, whereas prolactin levels rise. The lactiferous lobules' acini cells are stimulated to release milk by the prolactin hormone. The process is furthered by consuming enough fluids and food. When a baby suckers on the mother's nipple, the formed milk is gathered and drained from the lactiferous duct to the ampulla.
• Maintenance of secretion of milk or galactopoiesis: This is the process by which breasts continue to produce breast milk and maintain lactation after an infant suckes on the nipple and areola.
• Ejection of milk: This procedure happens after the baby has sucked on the breast. The following things happen for lactation while an infant suckes on the breast.

By using the dorsal nerve roots, activate the neuro-endocrine reflex in the brain's hypothalamus.

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Release of oxytocin into the blood by the posterior pituitary gland

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In alveoli, myoepithelial cells contract.

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Milk discharged into the lactiferous duct.

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The breast's ampulla collects milk, which also encourages the production of more milk.

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When a baby squeezes or suckers the breasts, milk is secreted for the baby.

Mechanism of Menstruation (Menstrual Cycle)

Menstruation is a cyclical process, and the menstrual cycle is the uterus preparing for a pregnancy. Every time a pregnancy fails, the endometrium deteriorates, and the cycle resumes. Normally, it happens every 28 to 30 days, but occasionally, it can happen every 21 to 42 days. The menstrual cycle involves three primary organs. Each organ has a unique cycle that it follows to complete the menstrual cycle.

• The pituitary gland
• The ovary and
• The uterus

Menstrual cycle refers to the time between the first and subsequent periods. The menstrual cycle entails a series of activities that take place at regular intervals over a duration of approximately 28 days and involve three phases:

• The proliferative phase
• The secretory phase
• The menstrual phase

Proliferative Phase

When menstruation is finished, the proliferative phase begins. The pituitary gland's anterior lobe secretes the follicle-stimulating hormone during this stage (FHS). This hormone causes the primordial follicle (ovarian follicle) to mature and become the graafian follicle. An ovum is contained within the follicle, and it also develops and grows. Typically, only one ovum develops and matures during these times. The cells of the follicle secrete estrogen during the ovarian follicle's growth and development.

This hormone encourages the columnar cell to divide the endometrium more quickly, resulting in a thicker lining and an increase in blood capillaries and glands, which gives the endometrium a more vascular and spongy appearance. From the fourth day of the previous menstruation, this phase can last up to 10 days. The endometrium is 4 to 10 mm thick by the time this phase is over.

The follicle bursts and the mature ovum emerges into the peritoneal cavity. Ovulation is the term used to describe the release of the ovum from the follicle. The mature (graafian) follicle ruptures as a result of the anterior pituitary's release of luteinizing hormone (LH). When ovulation occurs, this phase ends, and the secretary phase starts.

Secretary Phase

After ovulation, the secretary phase begins and lasts for around two weeks (14 days). The second ovarian hormone, progesterone, is secreted by the corpus luteum when the LH stimulates it. Progesterone increases estrogen's beneficial effects. The endometrial thickens even more as a result, and the blood capillaries in the surface endometrium enlarge. Large amounts of glycogen are secreted by the endometrial glands, which also start to secrete and enlarge and become more tortuous. In order to receive a fertilized ovum, the endometrium is now thick, spongy, moist, and more vascular. The endometrium is between 12 and 18 mm thick.

If the ovum is fertilized, the endometrium does not degrade and there is no menstrual flow. As a result, the endometrium is now known as decidua. The human chorionic gonadotrophin hormone that the fertilized ovum secretes keeps the corpus luteum healthy and enables it to continue secreting progesterone. This hormone is produced when the fertilized ovum embeds itself within the endometrium. In the absence of fertilization, menstrual bleeding starts.

Menstrual Phase

The corpus luteum ceases secreting progesterone and estrogen if the ovum is not fertilized, and it degenerates into a corpus albicans. Menstruation is brought on by the withdrawal of progesterone and estrogen, which induces the release of prostaglandins that constrict the spiral arterioles of the uterus. As a result, the endometrial cells start to lose oxygen and die. When capillaries break down, bleeding results from the endometrium's lining cells disintegrating and sloughing off. This persists for four to six days. Approximately 60-90m1 of blood should flow normally during each cycle. The pituitary gland resumes secreting the follicle-stimulating hormone when the blood progesterone level reaches a certain threshold. The next cycle begins after stimulating a new ovarian follicle.

Gametogenesis

Gametogenesis is the process through which sex cells are created. There is oogenesis in females and spermatogenesis in males, it is believed. Meiosis, a type of nuclear division, is involved in both.

Oogenesis

The development and differentiation of the female gamete or ovum through a meiotic division is known as oogenesis, also known as female gametogenesis. The development, maturation, processing, and release of gametes during puberty is known as oogenesis. In other words, it refers to the process by which female gametes, or ova, are formed in the ovaries of females. It is a cyclical process that yields just one ovum each month.

Puberty and Menopause

The physiological transitions of puberty and menopause occur at the start and conclusion of the female reproductive cycle, respectively. Puberty is a term that refers to the physical changes of sexual maturation rather than the behavioral and cultural facets of adolescent development (it is derived from the Latin word puberatum, which means age of maturity, manhood).

A child's body develops into an adult body during puberty, becoming ready for sexual reproduction and the ability to fertilize eggs. During this time, the potential for sexual reproduction is at its peak and secondary sex characteristics start to emerge.

Hormone signals to the gonads start this period. The gonads secrete hormones in response to hormones, which promote the development of the bones, muscles, blood, skin, hair, breasts, and reproductive organs. Growth quickens during the first half of puberty and slows down at the end.

Adolescence

The transitional era between childhood and maturity is one of psychological and social change. Puberty and adolescence typically coincide, albeit their limits are less clearly defined, and adolescence refers more to the psychosocial and cultural aspects of growth throughout the teen years than to the physical changes associated with puberty. Despite the wide range of normal ages, girls normally start the puberty process at age 10 or 11, whereas it starts in boys at around age 11 or 12. Boys typically reach puberty by age 16 to 18, while girls often reach it by age 15 to 17. About 4 years following the onset of the first physical changes associated with puberty, girls reach reproductive maturity.

Boys, on the other hand, grow more slowly but continue to do so for six years following the first noticeable pubertal changes. The main sex hormone for boys is an androgen called testosterone, whereas an estrogen called estradiol controls female development. Estradiol encourages breast and uterine growth and is the main hormone responsible for the pubertal growth spurt, epiphyseal maturation, and epiphyseal closure.

Conception

The process of fertilization and subsequent pregnancy establishment is known as conception. An ovum is fertilized to start a pregnancy, and the fetus is delivered once the baby is born. The many spermatozoa squirm around as sperm is implanted in the vagina. Some go to the ova and oviduct in the uterus to meet the eggs. Fertilization is the joining of sperm and eggs. Pregnancy begins on the day of fertilization and continues thereafter.

Climacteric and Menopause

The climacteric is the age-related irreversible decline of reproductive capacity. The cessation of menstruation, which typically occurs between the ages of 45 and 55, is the most obvious sign of climacteric in women.

The number of ovarian follicles decreases with age, and those that remain are less sensitive to gonadotropins. As a result, they produce less progesterone and estrogen. Without these hormones, menopause sets in and the uterus, vagina, and breasts begin to atrophy. Additionally, there is skin thinning, a decline in bone mass, and an increase in the risk of cardiovascular diseases. Some women also experience depression, irritability, and mood swings as a result of their changing hormonal profiles. Hormone replacement therapy, which involves administering low doses of estrogen and progesterone, is a common treatment for these symptoms.

Fertilization

Male and female gametes combine during the fertilization process to generate an embryo. The uterine tube's ampulla is a typical location. Only 1% of the sperm that is deposited in the vagina enters the cervix, which is moved with the help of uterine cilia and the sperm's own propulsion. Sperm loses its mobility after it crosses the isthmus and stops moving. The sperm can fertilize the ovum through the acrosomal reaction and capacitation processes.

Phases of fertilization:

Phase 1: Penetration of corona radiate: The combined effects of the tubal mucosal enzyme and capacitated sperm allow the sperm to enter the ova. Only one sperm fertilizes the ova; the remaining sperms likely aid in breaking through the barriers defending the female gamete.

Phase 2: Penetration of zona pellucid: Sperm can pass through the zona pellucid because of the release of acrosomal enzymes and acrosin during the acrosomal reaction.

• Sperm contact with the oocyte alters the zona's permeability by releasing lysosomal enzyme from the oocyte's plasma membrane.
• To stop further sperm penetration, this enzyme modifies the zona reaction, a feature of the zona pellucid.

Phase 3: Fusion of oocyte and sperm cell membrane

• The membranes covering the posterior region of the sperm and the oocyte actually fuse together during conception. During the acrosomal reaction, the acrosomal membrane vanishes.
• In a human, the plasma membrane stays outside while the head and tail of the sperm enter the oocyte.
• Following sperm entry, the egg reacts in three different ways:
  • Cortical and zona reaction.
  • Resumption of 2nd meotic division.
  • Metabolic activation of the egg.