Cell-cell communication It is no surprise that cells communicate with each other. Signaling is essential for coordinating the function and differentiation of nearby cells. Cells located close to one another communicate in three main ways: If the cells are connected by a gap junction, one cell can send a signal through the gap junction directly into the adjoining cell’s cytoplasm. If the cells are close enough…

Signal transduction The cell membrane is a barrier to the free movement not only of matter (molecules, ions), but also to that of information . Just as living cells must maintain an internal environment chemically separate from but in regulated exchange with the extracellular milieu, so too they must be informationally distinct inside and yet manage a connection with events outside, communicating with the extracellular world…

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Cell membrane structure and transport functions The contents of cells are sealed off from the extracellular environment by a lipid barrier called the plasma membrane that protects the cell’s interior from the changing conditions of the extracellular environment and helps maintain the specific chemical milieu supporting intracellular metabolic processes. This appendix contains additional background information about the structure and function of the plasma membrane. Proteins embedded…

Presentation: History and physical examination J.B is a 38 year old woman who presents to her primary care physician with a chief complaint of fatigue and weight gain. She was in her normal state of health until about 6 months ago. Since that time, she has been getting tired more easily and has lost over 12 pounds despite no significant change in her workout regime. In…

Introduction The male reproductive system has three principal functions: 1. The differentiation and maintenance of the primary and secondary sex characteristics under the influence of the hormone testosterone, made in the testes. 2. Spermatogenesis: The creation of the male gametes inside the testes. 3. The penile delivery of sperm from the testes into the female’s vagina in the act of procreation. This includes penile erection and…

The organs of pregnancy The placenta serves as the point of exchange between the circulatory systems of the mother and fetus; it is also a hormone-producing organ ( Fig. 35.1 A). The fully developed placenta is a round oval organ 15 to 20 cm in diameter and 2 to 3 cm thick, embedded in the uterine wall. It connects to the developing fetus via the umbilical…

Introduction The menstrual cycle defines the reproductive years of a woman’s life. It begins with menarche (the onset of menstruation) at about age 8 to 13 years and ends with menopause, which begins at about age 50 years. Evolutionarily, the purpose of each menstrual cycle is to create the opportunity for pregnancy. Preparation for potential pregnancy is achieved through two concurrent cycles, which together make up…

Introduction The word skeleton comes from the Greek skellein, meaning to dry up; a dried-up body (skeleton soma) is one with only the bones remaining. Thus etymologically, but also in our cultural imagination, our bones refer to death. However, the skeleton is, like any other organ system, a system dedicated entirely to the functions of life. The human skeleton is made not only of minerals, but…

Introduction Calcium plays a fundamental role in the physiology of all living organisms. At the macroscopic level, calcium is essential to maintaining the structural integrity of the skeleton. At the molecular level, calcium is central to several physiologic processes, including neurotransmitter release, signal transduction, and blood coagulation. Parathyroid hormone (PTH), the main product of the parathyroid glands, and vitamin D together regulate the serum calcium level.…

Introduction The adrenal gland plays a pivotal role in human endocrine physiology. It is subdivided into two sections, which function separately and originate from different embryonic tissues. The outermost shell of the adrenal gland, the adrenal cortex, is divided into three layers: 1. Zona glomerulosa 2. Zona fasciculata 3. Zona reticularis Together, these layers produce three kinds of steroid hormones: 1. Aldosterone, a mineralocorticoid, modulates electrolyte…

Introduction The thyroid—named from the Greek thureoeides , meaning “shield-shaped”—bears two essential responsibilities in the endocrine system: Maintains metabolic rate necessary for heat generation in warm-blooded species. Promotes normal growth and development from fetal life into childhood. Roughly 5% of the U.S. population has a diagnosed thyroid disorder, and perhaps another 5% has undiagnosed thyroid disease, according to the American Association of Clinical Endocrinologists. In developing…

Introduction The hypothalamus and pituitary gland constitute an elegant center of hormonal control known as the hypothalamic-pituitary axis (HPA). Each hormone controlled by the pituitary is regulated separately along its own pathway, or “axis.” The HPA integrates information from the body’s internal and external environments with higher cortical input. The HPA then orchestrates changes in the multiple physiologic systems controlled by the pituitary hormone axes, allowing…

Introduction In the 1920s, Frederick Banting and Charles Best isolated insulin and made possible the treatment and survival of millions of diabetics. This helped initiate the era of modern medicine, in which the empiricism of the 18th century and its practice in the 19th century came to fruition in the wondrous cures of the 20th century. This discovery was made possible by early research into pancreatic…

D.L. is a 9-year-old female who is being seen by her pediatrician for the fifth time this summer. She has been seen for multiple gastrointestinal (GI) complaints including abdominal pain, bloating, and frequent nausea. Her mother is worried because she continues to lose weight despite being given extra servings of food at meals and close monitoring. Presentation: History and physical examination D.L. has had multiple visits…

Introduction As described in Chapter 8 , the immune system is a complex cellular network that defends the body against danger. To do so, the immune system must distinguish between safe and dangerous substances. Safe or nonthreatening substances can be part of the body itself (e.g., normal extracellular molecules, cells, and tissues) or foreign (e.g., foods and commensal bacterial). Dangerous materials can be part of the…

Introduction The kidney modifies the contents of the plasma by filtering its components into the urine, whereas the liver modifies the blood contents by metabolically transforming them. The liver is where drugs, hormones, and toxic waste products, such as ammonia, are metabolized to inactive forms. The liver also plays an important role in carbohydrate metabolism. Specifically, the liver is involved in: Glycogen storage. Gluconeogenesis. Formation of…

Introduction In Chapter 24 , we saw that the acquisition of energy and building blocks requires digestion and absorption. We now focus on two other critical gastrointestinal (GI) capabilities, without which digestion and absorption could not occur: Motility is the muscular capacity for movement by which the digestive organs agitate food mechanically and propel it through the GI tract. Secretion is the process that delivers digestive…

Introduction The gastrointestinal (GI) system supplies the fuel and the building blocks for the functioning of the body through the digestion and absorption of nutrients. Its machinery for doing so is the alimentary canal, also called the gastrointestinal tract, a highly specialized long tube that connects the mouth and the anus. While providing for the absorption of essential nutrients and elimination of waste products, the GI…

C.J. is a 52-year-old male with chronic hypertension (HTN) managed both with lifestyle changes and pharmacologically. He presented yesterday morning to an outside hospital with malignant HTN, headache, and complaints of “tearing” chest pain. His only past medical history is labile HTN and borderline type 2 diabetes, he has never had surgery. Presentation: History and physical examination In the morning while walking to the bathroom, C.J.…