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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…

Transport of Acids and Bases

The lungs and the kidneys are largely responsible for regulating the acid-base balance of the blood (see Chapter 28 ). They do so by independently controlling the two major components of the body's major buffering system: CO 2 and ( Fig. 39-1 ). Chapter 31 focuses on how the lungs control plasma [CO 2 ]. In this chapter we see how the kidneys control plasma […

Urine Concentration and Dilution

Water Balance and the Overall Renal Handling of Water The kidney can generate a urine as dilute as 40 mOsm (one seventh of plasma osmolality) or as concentrated as 1200 mOsm (four times plasma osmolality) In the steady state, water intake and output must be equal ( Table 38-1 ). The body's three major sources of water are (1) ingested water, (2) water contained in the foods eaten,…

Transport of Potassium

Potassium Balance and the Overall Renal Handling of Potassium Changes in K + concentrations can have major effects on cell and organ function The distribution of K + in the body differs strikingly from that of Na + . Whereas Na + is largely extracellular, K + is the most abundant intracellular cation. Some 98% of the total-body K + content (~50 mmol/kg body weight) is inside…

Transport of Urea, Glucose, Phosphate, Calcium, Magnesium, and Organic Solutes

The kidney plays a central role in controlling the plasma levels of a wide range of solutes that are present at low concentrations in the body. The renal excretion of a solute depends on three processes—filtration, reabsorption, and secretion (see pp. 732–733 ). The kidney filters and then totally reabsorbs some of the substances we discuss in this chapter (e.g., glucose). Others, it filters and also…

Transport of Sodium and Chloride

The kidneys help to maintain the body's extracellular fluid (ECF) volume by regulating the amount of Na + in the urine. Sodium salts (predominantly NaCl) are the most important contributor to the osmolality of the ECF; hence, where Na + goes, water follows. This chapter focuses on how the kidneys maintain the ECF volume by regulating excretion of Na + and its most prevalent anion, Cl…

Glomerular Filtration and Renal Blood Flow

Glomerular Filtration A high glomerular filtration rate is essential for maintaining stable and optimal extracellular levels of solutes and water Qualitatively, the filtration of blood plasma by the renal glomeruli is the same as the filtration of blood plasma across capillaries in other vascular beds (see pp. 467–468 ). Glomerular ultrafiltration results in the formation of a fluid—the glomerular filtrate —with solute concentrations that are similar…

Organization of the Urinary System

The kidneys serve three essential functions. First, they act as filters, removing metabolic products and toxins from the blood and excreting them through the urine. Second, they regulate the body's fluid status, electrolyte balance, and acid-base balance. Third, the kidneys produce or activate hormones that are involved in erythrogenesis, Ca 2+ metabolism, and the regulation of blood pressure and blood flow. Functional Anatomy of the Kidney…