CoverModule 1.0. Homeostasis, Membranes, Electrophysiology and ANS1.1. Homeostasis1.1.1. Homeostasis Defined1.1.2. Homeostatic Control Systems1.1.3. Feedback Response Loop1.2. Cell Transport; Water & Solutes1.2.1. Fluid Compartments1.2.2. Osmosis1.2.3. Diffusion of Solutes1.2.4. Active Transport1.2.5. Bulk Transport1.3. Electrophysiology1.3.1. Ions and Cell Membranes1.3.2. Membrane Potentials1.3.3. Graded Potential1.3.4. Action Potentials1.3.5. Refractory Periods1.3.6. Propagation of an Action Potential1.4. The Synapse1.5. The Autonomic Nervous System1.5.1. Organization of the Nervous System1.5.2. Structural Organization of the ANS1.5.3. The SNS and the PNS1.5.4. The Enteric Nervous System1.5.5. Physiology of the ANS1.5.6. Neurotransmitters of the ANS1.5.7. Receptors of the ANS1.5.8. Actions of the Autonomic Nervous System1.5.9. Table of Actions for the SNS and PNS and Some Common DrugsModule 2.0. Skeletal Muscle and Special Senses2.1. Structural Organization of Skeletal Muscle2.2.1. Neuromuscular Junction, Excitation-Contraction Coupling2.2.2. Muscle Contractures and Cramps2.3. Whole Muscle Contraction, Fiber Type, Fatigue and Muscle Pharmacology2.3.1. Motor Units2.3.2. Factors that Influence the Force of Contraction2.3.2. Factors that Influence the Force of Muscle Contraction2.3.3. Energy Source for Muscle Contraction2.3.4. Skeletal Muscle Fiber Types2.3.5. Fatigue2.3.6. Muscle Pharmacology2.4. Smooth Muscle2.4.1. Smooth Muscle Contraction2.5. Control of Body Movement2.5.1. Voluntary Control of Muscle2.5.2. Reflexes2.6. Taste and Smell2.6.1. Taste2.6.2. The Sense of Smell2.7. Vision2.7.1. Structure of the Eye2.7.2. Focusing Light on the Retina2.7.3. Converting Light to Action Potentials2.7.4. The Retina2.7.5. Phototransduction2.7.6. Receptive Fields2.8. Hearing and Equilibrium2.8.1. The Nature of Sound2.8.2. The Hearing Apparatus2.8.3. Sound Vibrations to Action Potentials2.8.4. The Sense of Balance and EquilibriumModule 3.0. Cardiovascular System3.1. Structure of the Heart3.1.1. Chambers and Circulation3.2. Cardiac Cell Action Potentials3.2.1. Action Potentials in Cardiac Muscle Cells3.2.2. Action Potentials in Cardiac Autorhythmic cells3.2.3. Cellular Mechanisms of Inotropy and Chronotropy3.3. Electrophysiology of Heart Muscle3.3.1. Heart Conduction System3.3.2. Electrocardiogram (ECG)3.3.3. Abnormal ECG - Current of Injury3.4. The Cardiac Cycle3.4.1. Cardiac cycle3.4.2. Cardiac Measurements and Pressure Volume Loops3.5. Blood vessels and Blood Pressure3.5.1. Arteries and Veins3.5.2. Capillaries3.5.3. Blood Pressure Regulation and Shock3.5.4. Capillary Exchange3.5.5. Myogenic and Paracrine Regulation of Vasoconstriction and Vasodilation3.6. Blood3.6.1. Composition of Blood3.6.2. Hematopoeisis3.6.3. Breaking Down Red Blood Cells3.6.4. HemostasisModule 4.0. Urinary and Respiratory Systems4.1. Function and Structure of the Kidney4.1.1. Urinary System Function4.1.2. Functional Anatomy of the Urinary System4.1.3. The Nephron: Functional Unit of the Kidney4.1.4. The Renal Corpuscle: Bowman's Capsule4.2. Physiology of Urine Production4.2.1. Filtration4.2.2. Renal Clearance4.2.3. Tubular Reabsorption4.2.4. Urine Concentration and Dilution4.2.5. Hormonal Regulation of Urine Production4.3. Acid/Base Balance4.3.1. Buffers4.3.2. Acid/Base Disturbances4.4. The Respiratory System4.4.1. Respiratory System Structure and Function4.4.2. Respiratory Membrane4.4.3. Respiratory pressures and Inspriation/Expiration4.4.4. Alveoli and Surfactant4.4.5. Pneumothorax4.4.6. Pressure-Volume Loops and the Work of Breathing4.5. Gas Exchange and Transport4.5.1. Gas Laws4.5.2. Partial Pressure Gradients in the Lung4.5.3. Alveolar Gas Equation4.5.4. Oxygen and Carbon Dioxide Transport in the Blood4.5.5. Alveolar Ventilation4.5.6. Ventilation/Perfusion Ratio4.6. Chronic Bronchitis and Emphysema4.6.1. Respiratory Control by the Medulla Oblongata4.6.2. Chemicals that Regulate VentilationModule 5.0. Digestive, Endocrine and Reproductive Systems5.1. Functional Anatomy of the Digestive System5.1.1. Layers of the Digestive Tract5.1.2. Enteric Nervous System5.1.3. Organs of the Digestive System5.2. Digestion5.2.1. Carbohydrates5.2.2. Proteins5.2.3. Lipids5.2.4. Lipoproteins5.3. Regulation of Digestive Secretions5.4. Endocrine System5.4.1. Overview of the Endocrine System5.4.2. Hormone Receptors5.4.3. Hormones of the Body5.4.4. Other Hormones: Melatonin and Pheromones5.5. The Hypothalamus and Pituitary Gland5.5.1. Structure and Function of the Hypothalamus and Pituitary Gland5.5.2. The Posterior Pituitary5.5.3. The Anterior Pituitary5.5.4. Growth Hormone5.5.5. Prolactin5.5.6. Thyroid Hormones5.5.7. Adrenal Hormones5.6. Pancreas5.6.1. Insulin and Glucagon5.6.2. Diabetes Mellitus5.7. Reproductive System Anatomy5.7.1. Female Reproductive Anatomy5.7.2. Male Reproductive Anatomy5.7.3. Sexual Development at Puberty5.7.4. Male Reproductive Endocrine Axis5.7.5. Spermatogenesis5.7.6. Female Reproductive System: Oogenesis5.7.7. Ovulation and Fertilization5.7.8. The Ovarian Cycle5.7.9. The Uterine Cycle5.7.10. PregnancyAppendix A. GenderAppendix B. The Placebo EffectB.2.1. The Placebo EffectB.2.2. Examples of the Placebo EffectB.2.3. How do Placebos Work?B.2.4. Are Placebos Ethical?B.2.5. How do we validate actual effectiveness of placebosB.2.6. Tips for evaluating scientific evidenceB.2.7. What about Faith Healings
5.7.2

Male Reproductive Anatomy

image243.png
Lateral view of the Male Reproductive System
Author: OpenStax Anatomy and Physiology. License: Creative Commons Attribution License 4.0 license

The key components of the male reproductive system are shown in the image above. This system consists of a network of tubes that begins in the testes and eventually leads to the urethra, which then exits the body. Along the way are several accessory organs that contribute to the formation of the semen. Let's begin our discussion with the testes, the male gonads. Although they develop in the abdominal cavity, the testes are housed externally in the scrotum (we will explain how this happens later). This is essential for their function since sperm formation (spermatogenesis) requires a temperature slightly lower than normal body temperature. To assist in the regulation of temperature the walls of the scrotum contain a layer of smooth muscle, the dartos muscles, and the spermatic cord that passes through the inguinal canal contains skeletal muscle, the cremaster muscle.

These muscles can contract or relax depending on the outside temperature. When ambient temperature is warm the muscles relax allowing the testes to move away from the body to lower testicular temperature and when ambient temperature is cold they contract pulling the testes up against the body to increase temperature. The adult testes are ovoid organs about 4-5 cm long. They are housed in the scrotum and each is surrounded by a connective tissue sheath called the tunica albuginea. This sheath branches internally forming septa which divide the testes into numerous smaller compartments called lobules. Each lobule houses a long, highly coiled seminiferous tubule. It is within these tubules that spermatogenesis occurs. The tissue that surrounds the seminiferous tubules is the interstitial tissue and contains the cells that produce testosterone. These cells are the interstitial cells of Leydig or more commonly simply called the Leydig cells. The seminiferous tubules come together and converge into a system of ducts known as the rete testis, which further converges into a group of efferent ductules. The efferent ductules exit the testes and unite to form the epididymis.

The epididymis is a single, long, convoluted duct that forms a comma-shaped structure which sits on the surface of the testes. Although the sperm form in the seminiferous tubules of the testes, final maturation takes place in the epididymis. For example, sperm taken directly from the seminiferous tubules are not motile (they can't swim) and would not be able to move through the female system. Only after spending about 10-14 days in the epididymis do they become motile. The sperm remain in the epididymis until ejaculation. The epididymis is continuous with the vas deferens or ductus deferens. This duct exits the scrotum and passes through the inguinal canal into the abdominal cavity. In addition to the vas deferens and the cremaster muscles, the spermatic cord that passes through the inguinal canal also contains the testicular arteries and veins. Once in the pelvic cavity, the vas deferens runs up the anterior surface and then across the roof of the bladder to the posterior side of the bladder. As it begins to descend the posterior side of the bladder the tubes enlarge to form the ampulla of the vas deferens. The ampulla then unites with the ducts of the paired seminal vesicles forming the ejaculatory duct.

The seminal vesicles are the first of the accessory organs that contribute to the semen. They produce approximately 60% of the seminal fluid. The seminal vesicles provide several important components to the sperm. These include:

1) Fructose and citric acid to provide nutrients to fuel the sperm;

2) Fibrinogen that contributes to a weak, transient coagulation reaction once the semen enters the female tract which helps the semen adhere to the vaginal walls near the cervix as well as protecting the sperm from destruction by the acid environment of the vagina; and

3) Prostaglandins which help decrease the viscosity of the cervical mucus allowing the sperm to more easily enter the uterus. Prostaglandins also stimulate uterine contractions, helping the sperm move up the female tract.

The ejaculatory duct then enters the second of the accessory organs, the prostate gland, where it unites with the urethra. The prostate accounts for approximately 30% of the seminal fluid. Prostatic secretions include clotting factors that participate with the fibrinogen from the seminal vesicles in the coagulation reaction as well as fibrinolysis, which breaks down the clot and frees the sperm. In addition, the prostatic secretion has a high pH, which helps neutralize the acidic environment of both the male urethra and the female tract.

After the urethra exits the prostate it receives secretions from the last of the accessory organs, the bulbourethral glands, also known as Cowper’s gland, which contribute about 5% of the seminal volume. Secretions of the bulbourethral glands contain mucus to lubricate the urethra and buffers to neutralize acids in the urethra and vagina. The final 5% of the seminal volume is the sperm that comes from the epididymis.

The male urethra participates in both the urinary system and the reproductive system. Anatomically it is divided into three segments; the prostatic urethra exits the bladder and passes through the prostate gland; the membranous urethra passes through the muscles in the floor of the pelvic cavity and the spongy or penile urethra passes through the penis and opens to the exterior via the external urethral orifice. The final structure of the male reproductive system to be discussed is the penis. The penis is the male organ of copulation that is inserted into the female vagina during sexual intercourse. In performing this function, it is necessary that the penis become rigid. To make this possible the penis is composed of three parallel columns of erectile tissue, the two corpora cavernosa that run side by side just above the urethra, and the corpus spongiosum that surrounds the urethra. At the tip of the penis the corpus spongiosum expands to form the glans penis. We will discuss how these erectile tissues produce an erection later. In uncircumcised boys the glans penis is covered by the prepuce or foreskin. The prepuce is cut away during circumcision.

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