Key Concepts in Human Anatomy and Physiology

Perineum Anatomy

Perineum Structures

The perineum is a diamond-shaped space between the pubic symphysis (anteriorly), the coccyx (posteriorly), and the ischial tuberosities (laterally), lying just inferior to the pelvic diaphragm (levator ani and coccygeus).

It is divided transversely into two triangles:

• The anterior is the urogenital triangle, which includes the external genitals.
• The posterior is the anal triangle, which contains the anus.

The perineum is also divided into superficial and deep layers, with some muscles common to men and women.

Muscles of the Perineum and Pelvic Floor

Muscles making up the Urogenital and Anal (Pelvic) triangles/diaphragms include:

• Urogenital diaphragm: Superficial and intermediate planes
• Sphincters: Internal and external urethral and anal
• Bulbocavernosus or Bulbospongiosus
• Ischiocavernosus
• Deep and superficial transverse perineal muscles
• Pelvic diaphragm: Deep plane (levator ani and coccygeus)

The Levator ani muscle group includes:

• Puborectalis
• Pubococcygeus
• Iliococcygeus

Structures often associated with these regions (as seen in diagrams):

• Pubis
• Urethra
• Sacrum
• Coccyx
• Ischial tuberosity
• Vagina
• Vestibule
• Anus

Urinary System

Urinary System Functions

The primary function of the urinary system is cleansing the blood and the body of wastes. Additional, equally important functions include:

• Regulation of pH (a function shared with the lungs and the blood).
• Regulation of blood pressure (a role shared with the heart and blood vessels).

Micturition Center and Nerve Control

The micturition center is located in the sacral segment of the spinal cord, specifically between S2-S4.

Voluntary and involuntary micturition is controlled by the Hypogastric, Pelvic, and Pudendal (voluntary micturition) nerves.

Why Women Experience More UTIs

Women tend to have more urinary infections than men because of the shorter length of the female urethra, about 4 cm. This shorter length provides a smaller barrier to fecal bacteria compared to the longer male urethra.

Understanding the Micturition Reflex

The Micturition Reflex is a result of stretch receptors in the bladder wall that transmit nerve impulses to the sacral region of the spinal cord, generating a spinal reflex.

The resulting parasympathetic neural outflow causes contraction of the detrusor muscle and relaxation of the involuntary internal urethral sphincter. At the same time, the spinal cord inhibits somatic motor neurons, resulting in the relaxation of the skeletal muscle of the external urethral sphincter.

Digestive System

Mechanical Digestion Process

During the digestive process, mechanical digestion makes the food smaller to increase both surface area and mobility. This includes:

• Mastication (chewing) and tongue movements in the mouth.
• The mechanical churning of food in the stomach, which further breaks it apart and exposes more of its surface area to digestive juices, creating an acidic “soup” called chyme.

Pharynx and Esophagus Functions

The Pharynx propels food from the oral cavity to the Esophagus, which in turn propels food to the stomach.

Importance of the Mouth in Digestion

The mouth plays a crucial role in the digestive process:

• Ingests food.
• Chews and mixes food.
• Begins chemical breakdown of carbohydrates.
• Moves food into the pharynx.
• Begins breakdown of lipids via lingual lipase.

Ovarian Follicles

Factors Affecting Ovarian Follicle Count

Women are born with approximately 1 million follicles. During the aging process, they lose follicles. At puberty, they already have around 300,000 to 500,000 follicles. By 40 years old, women have only about 3% of their initial follicle count.

Factors that can decrease the quantity and quality of follicles include:

• Smoking
• Stress
• Poor diet
• Lack of exercise