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Cardiovascular System

Heart The primary component of the heart is the myocardium composed of cardiac muscle that has been described previously with the basic tissues. Briefly, cardiac muscle cells are elongated branched cells with centrally located, round or oval nuclei, many cells are binucleated. Cytoplasm is eosinophilic and features cross striation; cell boundaries are prominent lines identified as intercalated discs. The innermost surface of the cardiac wall is…

Lymphatic System

Lymphatic follicles Lymphatic follicles (lymphatic nodules) are spherical or ovoid structures composed of aggregated lymphocytes and a meshwork of reticular cells. Lymphatic follicles lack capsule, and they typically populate the lamina propria of the mucous membranes in the alimentary (gut-associated lymphoid tissue, GALT) and respiratory tracts (bronchus-associated lymphoid tissue, BALT). Primary follicles are mostly composed of small lymphocytes, while secondary follicles contain a central light zone,…

Basic Tissues

Epithelium Functionally, epithelium can be subdivided into two main types: covering (surface) epithelium and glandular epithelium. Surface epithelium covers mucous and serous membranes of tubular (hollow) organs as well as the outer surface of the body as epidermis. Structurally, surface epithelium can be composed of a single layer of epithelial cells (simple epithelium) or multiple layers of cells (stratified epithelium). Epithelial cells forming the simple epithelium…

FERTILIZATION, PLACENTATION AND LACTATION

FERTILIZATION Sperm capacitation ( 23-1 ) Fertilizing sperm must complete maturation and capacitation before sperm-egg fusion can take place. Sperm released from the testis and entering the epididymal duct display circular motion . After a 2-week maturation process during epididymal transit, sperm acquire forward motility , a maturation step required for fertilization. After ejaculation, a number of sperm undergo a capacitation process in a storage site…

FOLLICULOGENESIS AND MENSTRUAL CYCLE

Development of the female reproductive tract The reproductive tract develops through the differentiation of wolffian ducts (male reproductive tract anlage) and müllerian ducts (female reproductive tract anlage). The female reproductive system consists of the ovaries , the ducts (oviduct, uterus and vagina) and the external genitalia (labia majora, labia minora and clitoris) . Knowledge of the developmental sequence from the indifferent stage to the fully developed…

SPERM TRANSPORT AND MATURATION

DEVELOPMENT OF THE GONADS ( Primer 21-A ) An important aspect of gonadogenesis is the migration of cell precursors of the male and female gametes from the primary ectoderm into the wall of the yolk sac to become extra-embryonic . Bone morphogenetic protein , together with signals from the extraembryonic mesoderm and visceral endoderm, specifies pluripotent epiblast cells to become primordial germinal cells (PGCs) . PGCs…

SPERMATOGENESIS

THE TESTES ( 20-1 and 20-2 ) The testes are paired organs located in the scrotum, outside the abdominal cavity. This location enables maintenance of the testes at a temperature 2 o C to 3 o C below body temperature. A temperature of 34 o C to 35 o C is essential for normal spermatogenesis . The posterior surface of the mature testis is associated with…

ENDOCRINE SYSTEM

THYROID GLAND Development of the thyroid gland The thyroid gland (Greek thyreos , shield; eidos , form) develops as a median endodermal downgrowth at the base of the tongue. A transient structure, the thyroglossal duct , connects the developing gland to its point of origin, the foramen cecum , at the back of the tongue. The thyroglossal duct disappears completely, leaving the thyroid to develop as…

NEUROENDOCRINE SYSTEM

HYPOPHYSIS ( 18-1 ) The hypophysis (Greek hypo , under; physis , growth), also known as the pituitary gland , consists of two embryologically distinct tissues: 1. The adenohypophysis , the glandular epithelial portion. 2. The neurohypophysis , the neural portion. The adenohypophysis is formed by three subdivisions or parts: 1. The pars distalis , or anterior lobe , is the main part of the gland.…

DIGESTIVE GLANDS

STRUCTURE OF A SALIVARY GLAND ( 17-1 and 17-2 ) We start the discussion by reviewing the general organization and function of a salivary gland, in particular its branching ducts (see Box 17-A ). An initial discussion concerning the general features of a compound or branched gland is included in Chapter 2, Epithelial Glands | Cell Biology. Box 17-A Classification of exocrine glands Depending on the…

LOWER DIGESTIVE SEGMENT

SMALL INTESTINE ( 16-1 to 16-3 ) The 4- to 7-meter-long small intestine is divided into three consecutive segments: 1. Duodenum . 2. Jejunum . 3. Ileum . The duodenum is about 25 cm in length, is mainly retroperitoneal and surrounds the head of the pancreas. At its distal end, the duodenum is continuous with the jejunum, a movable intestinal segment suspended by a mesentery. The…

UPPER DIGESTIVE SEGMENT

Mouth (oral cavity) The oral cavity is the entrance to the digestive tube. Ingestion, partial digestion and lubrication of the food, or bolus, are the main functions of the mouth and its associated salivary glands. We study the salivary glands in Chapter 17 , Digestive Glands. The mouth, or oral cavity, includes the lips, cheeks, teeth, gums (gingivae), tongue, uvula and palate. The various regions of…

URINARY SYSTEM

THE KIDNEYS ( 14-1 ) The urinary system consists of paired kidneys and ureters and a single urinary bladder and urethra. Each kidneys has a cortex (subdivided into outer cortex and juxtamedullary cortex) and a medulla (subdivided into outer medulla and inner medulla) . The medulla is formed by conical masses, the renal medullary pyramids , with their bases located at the corticomedullary junction. A renal…

RESPIRATORY SYSTEM

THE RESPIRATORY SYSTEM Nasal cavities and paranasal sinuses ( 13-1 ) The nasal cavities and paranasal sinuses provide an extensive surface area for: 1. Warming and moistening air. 2. Filtering dust particles present in the inspired air. In addition, the roof of each nasal cavity and part of the superior concha contain the specialized olfactory mucosa . Each nasal cavity, separated from the other by the…

CARDIOVASCULAR SYSTEM

THE CARDIOVASCULAR SYSTEM ( 12-1 ) The circulation is divided into the systemic or peripheral circulation and the pulmonary circulation . Arteries transport blood under high pressure and their muscular walls are thick. The veins are conduits for transport of blood from tissues back to the heart. The pressure in the venous system is very low and the walls of the veins are thin. There are…

INTEGUMENTARY SYSTEM

ORGANIZATION AND TYPES OF SKIN ( 11-1 ) The integument is the largest organ of the body. It consists of two components: 1. The skin . 2. The epidermal derivatives , such as nails, hair and glands (sweat and sebaceous glands and the mammary gland). The skin has several functions: 1. Protection from injury (mechanical function). 2. As a water barrier to prevent dehydration. 3. Regulation…

IMMUNE-LYMPHATIC SYSTEM

COMPONENTS OF THE IMMUNE–LYMPHATIC SYSTEM ( 10-1 and 10-2 ) The lymphatic system includes primary and secondary lymphoid organs . The primary lymphoid organs produce the cell components of the immune system (see 10-1 ). They are: 1. The bone marrow . 2. The thymus . The secondary lymphoid organs are the sites where immune responses occur. They include: 1. The lymph nodes . 2. The…

NERVOUS TISSUE

Development of the nervous system ( 8-1 and 8-2 ) The central nervous system (CNS) develops from the primitive ectoderm (see 8-1 ; see Box 8-A and Box 8-B ). A simple epithelial disk, the neural plate , rapidly rolls into a hollow cylinder, the neural tube . This process is known as neurulation . Box 8-A Ectoderm germ cell layer The ectoderm germ cell layer…

MUSCLE TISSUE

SKELETAL MUSCLE ( 7-1 ) Muscle cells or fibers form a long multinucleated syncytium grouped in bundles surrounded by connective tissue sheaths and extending from the site of origin to their insertion. The epimysium is a dense connective tissue layer ensheathing the entire muscle . The perimysium derives from the epimysium and surrounds bundles or fascicles of muscle cells. The endomysium is a delicate layer of…