When holding urine, there are two primary sphincters that help control the release of urine. The internal urethral sphincter is composed of smooth muscle, and is therefore not consciously controlled. The external urethral sphincter is composed of skeletal muscle, which means that it can be consciously controlled.

The detrusor muscle is the smooth muscle found in the walls of the bladder. When contracted, this muscle leads to urination. The rectus abdominis is a region of the abdominal wall. When contracted, this muscle can indirectly assist in urination by reducing the volume of the abdominal cavity and pressuring the bladder.

Because women have smaller urethras, bacteria and other pathogens have a shorter distance to travel in order to cause infections in the body. In addition, the proximity of the anus to the urethral opening in women is much closer compared to men, resulting in a closer proximity to bacteria.

Total body water is approximately 60% of body weight. The percentage of total body water is highest in newborns and adult males, and lowest in adult females and in adults with large amounts of adipose tissue (fat). Intracellular fluid is 40% of body weight, and extracellular fluid is 20% of body weight (60-40-20 rule).

Intracellular fluid (ICF) is two-thirds of total body water. Its major cations are  and . The major anions of ICF are proteins and organic phosphates (ATP, ADP, AMP). Also, most proteins carry a net negative charge at physiological pH. Major cations of extracellular fluid (ECF) are , its anions are  and . Remember that the sodium potassium pump works continuously to pump three sodium ions out of the cell and two potassium ions into the cell, thus concentrating these species in their respective compartments.

Extracellular fluid (ECF) contains the cation , and  and  as its anions.  ECF is one-third of total body water and is composed of interstitial fluid and plasma. Plasma is one-fourth of the ECF, thus it is one-twelfth of total body water (TBW).

Intracellular fluid (ICF) provides two-thirds of TBW. Its major cations are  and . The major anions of ICF are proteins and organic phosphates (ATP, ADP, AMP). Note that DNA also carries a net negative charge, and is intracellular, but not dissolved.

Saliva contains the enzyme alpha amylase. This enzyme is responsible for breaking down starch and carbohydrates into smaller polysaccharide chains.

Later, in the small intestine, pancreatic beta amylase further digests the carbohydrates until they can be absorbed into the blood. Most chemical digestion occurs in the small intestine, where enzymes to digest proteins, lipids, and carbohydrates are introduced to the digestive tract.

The mouth is the start of the gastrointestinal tract. It is the site of both mechanical and chemical digestion via chewing, and saliva, respectively. Saliva contains the enzyme amylase that breaks down carbohydrates. 

The correct answer is mouth. While each answer choice has a part in the digestion process, carbohydrate digestion begins in the mouth, which provides enzymes required for starch (amylase) and sugar (lactase, maltase, sucrase) digestion.

Carbohydrate digestion (starches and sugars) begins in the mouth with the enzyme salivary amylase. Amylase, which is also found in the small intestine, is responsible for breaking apart starches. Sugars are also digested (broken down) by three major enzymes located in the mouth and small intestine (lactase, maltase, sucrase). The carbohydrates are broken down along the gastrointestinal tract (mouth, pharynx, esophagus, stomach) and are absorbed while moving through the small intestine.

Styloglossus: elevates and retracts tongue

Hyoglossus: depresses and retracts the tongue

Palatoglossus: elevates the tongue

Vertical muscles: this is an intrinsic muscle of the tongue

"Deglutition" is the scientific term for swallowing. In contrast, the scientific term for chewing is "mastication." The scientific term for urination is "micturition." Lastly, "voiding" is also another word for urination.