The path of urine excretion from the body, after filtrate passes through the collecting ducts of the nephrons, begins in the renal pelvis. The renal pelvis collects the concentrated filtrate and transfers it to the bladder via the ureters. During urination, the bladder contracts, and urine exits the body through the urethra.

Vasa recta are capillaries found near nephrons within the kidneys. 

The ureters extend from the kidneys to the urinary bladder, where urine is stored until it can be excreted from the body.

The loop of Henle, distal tubule, and collecting duct are all considered parts of the nephron and are involved in filtration and concentration of urine. After passing through the collecting duct, urine enters the ureters for transport to the bladder. From the bladder, urine enters the urethra before expulsion from the body.

The urinary bladder is an important structure in humans that stores urine until urination. The walls of the bladder contain both smooth and somatic muscle. The smooth muscle serves to detect the degree of stretch of pressure in the bladder, stimulating the sensation of a full bladder and the need for urination. The somatic muscle allows for actual contraction of the bladder, making urination a voluntary process.

Without a bladder, the urine from the kidneys would continuously flow to the ureter and, subsequently, to the urethra where it would be excreted. Due to this continuous flow, urine would not be stored, and the person will have to urinate constantly. This means that without a urinary bladder, urination will become involuntary and the individual will urinate constantly (urination frequency will increase dramatically).

After exiting the collecting duct, urine enters the renal pelvis. The renal pelvis is part of the ureter and is found inside the medulla of the kidney. Numerous collecting ducts will pool into the renal pelvis, allowing urine to accumulate. After it exits the kidney (via the renal pelvis), urine enters the ureter where it is pushed towards the urinary bladder. In the bladder, urine is stored until it reaches a maximum threshold pressure and volume. Once this maximum is reached, the individual feels the urge to urinate and the process of urination begins. During urination, the urine is propelled via smooth muscle contraction from the urinary bladder to the urethra, and excreted from the body.

The basement membrane is negatively charged in order to repel other negatively charged substances, specifically proteins. This is important because it ensures that proteins don't enter the filtrate, which is eventually excreted as urine. Old or malfunctioning proteins can be broken down, and their amino acids can often be recycled. Excretion of protein molecules would be extremely unfavorable.

An obstructive kidney stone in a nephron would impact bulk forces and filtration. Specifically, it would affect the hydrostatic pressure in Bowman's capsule. As a result, the glomerular filtration rate would decrease due to increased hydrostatic pressure in the capsule opposing filtration. Consequenty, fluid would be prevented from being filtered out of the kidney.

The papillary duct forms from collecting ducts in the kidney, where it travels to the calyces in the renal pelvis and then out of the kidney (via the ureter) to the bladder. Here, it is stored until micturition (urination).

While internal and external sphincter muscles are used to expel waste, these are located in the anal canal, not the rectum. The rectum precedes the anal canal and serves as storage; it signals the nervous system when it is full and defecation is needed.