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Regulation of Body Temperature

Heat and Temperature: Advantages of Homeothermy Homeotherms maintain their activities over a wide range of environmental temperatures The ability to regulate internal body temperature has provided higher organisms independence from the environment. Because the rates of most physical and chemical reactions depend on temperature, most physiological functions are sensitive to temperature changes. Thus, the activity levels of poikilotherms (species that do not regulate internal body temperature)…

Metabolism

Metabolism encompasses all chemical reactions in the body's cells, necessary to sustain life. These chemical processes allow the body to grow, reproduce, maintain structure, and respond to changes in its environment. These processes can be anabolic, in which energy is used in the formation of substances such as proteins or nucleic acids, or catabolic, in which organic substances are broken down during cellular respiration to harvest…

Fetal and Neonatal Physiology

Fetal development is a highly organized process. The most rapid phase of growth transpires in at a degree of hypoxemia that mimics ascent to Mount Everest, while nutrients reach the fetus indirectly, from the maternal circulation. The transition to the extrauterine environment occurs abruptly and is likewise extraordinarily well orchestrated. Indeed, within a matter of seconds, the breathing infant can supply sufficient oxygen to the tissues…

Fertilization, Pregnancy, and Lactation

Transport of Gametes and Fertilization Cilia and smooth muscle transport the egg and sperm within the female genital tract Following ovulation, the fimbriae of the fallopian tube sweep over the ovarian surface and pick up the oocyte—surrounded by its complement of granulosa cells, the cumulus oophorus, and corona radiata (see p. 1122 )—and deposit it in the fallopian tube. Shortly after ovulation, movements of the cilia…

The Female Reproductive System

The female reproductive system functions to (1) pro­duce haploid gametes— ova, (2) facilitate syngamy —or fertilization—between an ovum and a spermatozoon, (3) supply a site for implantation of the embryo (if syngamy occurs) and the establishment of pregnancy, (4) provide for the physical environment and nutritional needs of the developing fetus and its timely birth, and (5) nurture the neonate. The system consists of the gonads…

The Male Reproductive System

The male reproductive system consists of two essential elements: the gonads (in this case the testes) and the complex array of glands and ducts that constitute the sex accessory organs ( Fig. 54-1 A, B ). Open full size image Figure 54-1 Anatomy of the male internal genitalia and accessory sex organs. A, The two major elements of the male sexual anatomy are the gonads (i.e.,…

Sexual Differentiation

Reproduction is a fundamental process of life. All living organisms must reproduce either asexually (e.g., bacteria) or sexually (e.g., mammals). Asexual reproduction is highly efficient and produces large numbers of genetically identical offspring in a relative short amount of time. This strategy, however, is vulnerable to environmental changes because genetic and phenotypic variation between individual progeny is minimal and consequently the probability of producing progeny that…

The Parathyroid Glands and Vitamin D

Calcium and Phosphate Balance Calcium plays a critical role in many cellular processes, including hormone secretion, muscle contraction, nerve conduction, exocytosis, and the activation and inactivation of many enzymes. As described in Chapter 3 , calcium also serves as an intracellular second messenger by carrying information from the cell membrane into the interior of the cell. It is therefore not surprising that the body very carefully…

The Endocrine Pancreas

The islets of Langerhans are endocrine and paracrine tissue The pancreas contains two types of glands: (1) exocrine glands, which secrete digestive enzymes (see p. 882 ) and (see pp. 885–886 ) into the intestinal lumen; and (2) endocrine glands, called the islets of Langerhans. The islets are spread throughout the pancreas and in aggregate comprise only 1% to 2% of its tissue mass. The normal…

The Adrenal Gland

The human adrenal glands, each weighing only ~4 g, are located above the upper pole of each kidney in the retroperitoneal space. They produce four principal hormones: cortisol, aldosterone, epinephrine (adrenaline), and nor­epinephrine. Each adrenal gland is composed of an inner medulla and an outer cortex ( Fig. 50-1 ). Embryologically, the cortex is derived from mesoderm, whereas the medulla is derived from neural crest cells (see…

The Thyroid Gland

The thyroid gland is located in the anterior neck, lying like a small bow tie across the front of the trachea. In adults, the normal thyroid weighs ~20 g. It is composed of left and right lobes and a small connecting branch, or isthmus. The thyroid gland possesses many features unique among endocrine glands, not the least of which is that it is the only endocrine gland…

Endocrine Regulation of Growth and Body Mass

Growth from the fertilized ovum to the adult is an exceedingly complex process involving both hyperplasia (an increase in the number of cells) and hypertrophy (an increase in the size of cells) as well as turnover of the cellular elements of body tissues. The timing and capacity for cell division vary among tissues. In the human central nervous system (CNS), neuronal division is essentially complete by…

Organization of Endocrine Control

With the development of multicellular organisms that have specialized tissues and organs, two major systems evolved to communicate and coordinate body functions: 1 The nervous system integrates tissue functions by a network of cells and cell processes that constitute the nervous system and all subdivisions, as discussed in Chapter 10 , Chapter 11 , Chapter 12 , Chapter 13 , Chapter 14 , Chapter 15 ,…

Hepatobiliary Function

Overview of Liver Physiology After the skin, the liver and the brain are the largest organs in the human body. The liver weighs between 1200 and 1500 g, representing 2% to 5% of body weight in the adult and ~4% to 5% in the newborn. The liver is strategically situated in the circulatory system to receive the portal blood that drains the stomach, small intestine, large intestine,…

Nutrient Digestion and Absorption

In general, the digestive-absorptive processes for most of the constituents of our diet are highly efficient. For example, normal adult intestine absorbs ~95% of dietary lipid. How­ever, we ingest most of the constituents of dietary food in a form that the intestine cannot readily absorb. Multiple digestive processes convert dietary food to a form that can be absorbed—primarily in the small intestine, but also, to a…

Intestinal Fluid and Electrolyte Movement

Functional Anatomy The small intestine and large intestine have many similarities in structure and function. In some cases, different regions of the intestinal tract carry out certain functions in much the same manner. In other cases, however, substantial heterogeneity exists between different intestinal segments (e.g., ileum versus jejunum) or between different mucosal areas (e.g., villus versus crypt) in one intestinal segment. As discussed in Chapter 41…

Pancreatic and Salivary Glands

Overview of Exocrine Gland Physiology The pancreas and major salivary glands are compound exocrine glands The exocrine pancreas and major salivary glands are compound exocrine glands—specialized secretory organs that contain a branching ductular system through which they release their secretory products. The principal function of these exocrine glands is to aid in the digestion of food. The saliva produced by the salivary glands lubricates ingested food…

Gastric Function

The stomach plays several important roles in human nutrition and has secretory, motor, and humoral functions. These activities are not separate and distinct, but rather represent integrated functions that are required to initiate the normal digestive process. The stomach has several specific secretory products. In addition to the stomach's best-known product, acid, these products include pepsinogen, mucus, bicarbonate, intrinsic factor, and water. These substances continue the…

Organization of the Gastrointestinal System

Overview of Digestive Processes The gastrointestinal tract is a tube that is specialized along its length for the sequential processing of food The gastrointestinal (GI) tract consists of both the series of hollow organs stretching from the mouth to the anus and the several accessory glands and organs that add secretions to these hollow organs ( Fig. 41-1 ). Each of these hollow organs, which are…

Integration of Salt and Water Balance

Two separate but closely interrelated control systems regulate the volume and osmolality of the extracellular fluid (ECF). It is important to regulate the ECF volume to maintain blood pressure, which is essential for adequate tissue perfusion and function. The body regulates ECF volume by adjusting the total-body content of NaCl. It is important to regulate the extracellular osmolality because hypotonic (see pp. 131–132 ) or hypertonic…